2024 GM 6.6L L8T Gas V8 + Allison Versus 6.6L Gen2 L5P Diesel V8: Which One Is The Better Buy? 

My parents have been RV'rs for 40+ years. Class A Motor Home flat towing a MidSize Truck, Class C Motor Home, 37' 5th Wheel with Triple Slides, and anything in between 19-27' conventional travel trailers with single and dual slide outs. One thing all had in common - GAS ENGINE. They've been all over the US and towing up mountain passes and across the desert. They have never been stranded or broken down. The longest trailer was a 37' 5th wheel trailer towed behind a Chevrolet 3500 HD (not dually) with a Gas Engine. I've always asked him why he didn't go for Diesel. Primary it comes down to maintenance costs on a diesel . It is more than just fuel costs and until recently Diesel was 60 cents to a $1.5 more. Even if Diesel fuel drops below Gas Prices you still have a lot more maintenance in that diesel. Unless you are towing heavy loads every day you don't need a diesel. But even then.... I have a friend that owns a steel business and he used to maintain a fleet of diesel 1 ton trucks to haul around their gooseneck trailers. Guess What - he moved over to gas 1 ton trucks because the maintenance on the Diesels were outrageous. This is real world experience coming from someone that is all about maximizing profit. And they all ran 87 octane all day every day (at altitude you actually can use lower octane not higher although I'd stick with the 87). I think too many people just like the coolness of the Diesel. Just about every video I've watch they bash the gasser. Most of us will be driving that truck as a daily driver with nothing but ourselves or a few passengers in it for 95% of the time. So ask yourself do you really need to fork out almost another 10k to the cost of the truck and deal with the headaches and expense that comes with a diesel for that other 5% of the time?

I have a 24 Denali 3500HD diesel. Crippling issues with the DPF system and I’m not alone. No fix and no eta. Go gas you still get the 10 speed Allison.

Went with a gas 3500 because I knew that I wouldn't be working a deseil very hard or often. All the travel trailers I'm interested are less than 7000 lbs GVWR, so even pulling grades at high altitude shouldn't be an issue. I like having more truck than trailer 😊.

For 98% of people the gas is plenty, also the diesels arnt what they used to be, most are NEVER gonna last as long as they used to.

I have a 2004 GMC 2500HD and just went over 400k miles and still runs like a champ. Only use it to pull travel trailer to hunt or camp in Az. I do want a new GMC Diesel but geeeezus the prices are just insane. Love you channel keep up the great work

Holy crap! Gas is expensive there. Definitely cheaper to run gas over diesel on the East Coast. Gas is 70-80 cents a gallon cheaper than diesel here. The reason you don't have 87 octane is due to the altitude. 85 is equivalent to 87 at altitude.

I feel like the gas versus diesel debate is similar to the 2500 versus 3500. I bought a 2500 thinking that would be enough capacity for me. Turns out a few years later that it wasn’t. I feel like if I buy a gas I would be wishing I had the extra towing capability of the diesel a few years later. I’d say just be certain you have no plans to change your current needs before you plan on replacing your vehicle. 🇺🇸💪

I feel like if they added a turbo to the gasser from the factory it would definitely close the gap between the two..

Just towed my 37.5’ fifth wheel from Florida to Michigan. 14,000 lbs. 2024 L8T gas’s and it preformed great. Until now I have always towed with diesel. Totally satisfied with the gasser. Keep in mind we are older and will be towing only on occasionally so absolutely o need for a diesel. By the way, 8.3 mpg over 1448 miles.

Vehicle prices are ridiculous! I normally buy a new truck every two years but I'm holding off for awhile to see if they will start coming down in price!

I’ve towed with the old Lq4 gm trucks and it’s not very fun. The motor is screaming most of the time I understand that the 10 speed will help with that but towing with a diesel is so much more enjoyable. I couldn’t go back to a gas after owning a diesel but hey it’s not my money do whatever you want.

Love the content, keep it coming! I've read that the Pedal Commander really wakes up the 6.6 gasser.

I agree with you JB. I live at 7000ft elevation. My only gripe is that the modern diesel is not as proven in reliability as old diesels. It’s more so the emissions and fuel system as they are very high pressures now. Can replace the 6.6 gas motor for the cost of replacing 8 fuel injectors on L5P. Let’s see what the supercharger Whipple is about to release for the L8T does for the gasser.

Don't let the "Allison" fool you. The transmission is built by GM. They're just using the "Allison" name to get you thinking that it's an Allison-built transmission......it's not.

So glad you mention the inadequacy of a normally aspirated gasoline engine for towing at altitude. I was once towing with a gas ford 5.4L v8 at close to 10k ft elevation with the gas pedal to the floor doing 10mph. A 3k lbs trailer!!!! The diesel cost is worth every penny!

A good video, good information. My experience with my older Chevy gas and diesel trucks a 2001 Chevy 2500HD 6.6 Allison transmission, Duramax lb7 101,000 miles 330hp and 585lbs of torque with the K&N cold air breather and 3.73 rear gears, 22mpg highway and 15.5 mpg city. My Chevy 2004 3500 crewcab dually 8.1L gas ( 496ci ) Allison transmission 4.10 rear gears, 450lbs of toque, 330 hp , 265,000 miles (runs great) 10 mpg highway and 9 mpg city. My 2004 3500 gas dually will haul a heavy load with more stability then my 2500 Duramax. I plan on put a K&N cold air breather on my 8.1 gas . Both are great trucks and never plan on selling either one of them. I do have another Chevy 2500 with the gas 6.0 3.73 rear gears and 365hp and 375lbs of toque. It good for lighter loads . 214,00 miles on the engine. The price of gas here in Kentucky this week is $2.99 for regular and diesel is $3.99 a gallon . If your going to buy a new truck the 6.6 gas will be great in a 2500hd with all the power the 6.6 produces today, I see no reason going extra for a Duramax in a 2500hd a few years ago yes because the 6.0 and 6.2 wasn’t as powerful. They stopped putting in the powerful gas 8.1L in 2006 or 07. Big mistake. The best big block bulletproof ever built by any company.

Depends on where you tow, how many miles a week and weight, on mostly flat land no more than 250 miles a week and 12,000 pounds or less then gas will be fine

Great video brother! I just ordered a 24 diesel to replace my 06 LBZ I’ve driven for 17 years. It’s been trouble free 300,000 miles. I’m a little nervous but with good maintenance I’ll hope I can avoid some emissions problems. Keep up the good work.

Appreciate the comparison. It was needed. Now for the duallies.

my horses are worth more than a dozen trucks to me. so I'm towing them with a diesel truck because it controls the trailer better than a gas truck. it means my horses are safer during transit. I'll deal with the emissions if it crops up. horses are more important to me

I know this is an old video but man what a difference. Diesel here has been running 4-4.50 a gallon vs 87 octane gas has been like 2.65-3.25. That’s why it’s a makes more sense. Also Indiana is flat as heck so I don’t need the torque. 😂

JB, I understood what you were putting down on octane ratings. My question is, would you have bought the gas 3500 if you were doing moderate towing?

I think that's the only place I've seen diesel cheaper than gas in years!

For the price i would get the ethanol free. It gets you over the 87 octane and ethanol has lower fuel density so it requires more for the same power. You should get a bump in mpg with ethanol free. Maybe ill do and experiment on my L8T. Problem is, 87 in Florida is $3.30 and ethanol free is another $1. Good content, cant wait to see your driving impressions on the gasser.

What is your opinion on a gas 3500 dually vs a 3500 dually diesel

I'd have to go with the gas. Just because it's less maintenance than a diesel engine. Don't get me wrong, I do love diesel.

That diesel price. Diesel here in KY where I am is over 1.00 a gallon more than gas. Just paid 4.19 for diesel and gas is 2.99 for 87 octane. I’ve never seen these octane ratings before. Thanks for the content!!!

So I mean this as nice as possible, but I think you’re just wasting your time with the 6.6 gas truck. I just don’t think your diesel fandom is going to allow you to even give it a fair chance. Just my opinion. Anyways, so any engine pulling a grade HAS TO turn an rpm that is somewhere close to its peak horsepower in order to maintain highway speeds (60 mph and up let’s say). For a gas engine, that number is typically above 5000 rpm. The L8T is like 5200, the 7.3 Ford is 5500. So naturally they need to be somewhere around 5000 rpm on a steep grade to maintain speed because contrary to what anyone says, HORSEPOWER determines the speed you’re going to pull a grade, not torque. So this same thing happens with diesels. They have to get somewhere close to their peak horsepower to do highway speeds on grades. The diesel that number is just a lot lower but diesel engines just naturally won’t rev like a gas engine. So the diesel hp peak may be 2800 or 3000 rpm. But you can be rest assured towing on a steep grade the diesel is going to be somewhere in that vicinity. So I just don’t understand why people want to dog a gas engine for “screaming” when by design they have to turn that rpm to go highway speeds on a grade towing. Just like the diesel has to turn an rpm close to its peak HP to do the same. I’m just not even going to bother with the gearing. I mean just go test drive a Ford with the 4.30 and tow you’re black trailer on a steep grade and do 60-70 mph. I will bet you $100 to a doughnut that you’re going to be in a gear (probably 4th or 5th) that puts the engine at 4500ish rpm. Then go back and test one with a 3.55 or 3.73 and I’ll let you go double or nothing to try and get your doughnut back that you will be in a gear (one gear lower than the 4.30 was so probably 3rd or 4th) and you will be at 4500ish rpm to maintain the speed. That’s the purpose of the modern transmissions. The 4 something gear is doing you absolutely zero benefit at Highway speeds and it is physically impossible for it to pull a grade in the same gear as the 3.55 or 3.73 because you will be rpm limited based on the speed and the computer will not allow the downshift.

You can now supercharge the L8T 6.6 and still not cost anymore than a diesel without all the diesel headaches which would make a big difference at high altitudes.

If you're towing daily and long distances, diesels are the way to go. Everything else, gas is probably the best choice.

Another added cost in Ontario Canada is your plate tag. Due to the stock weight of the truck it costs $285/year for the diesel vs $0/year for the gas truck.

That is a beautiful color on that diesel!

This is great information as always, Love the video!

I was a huge fan of a diesel in the 80s and 90s, but all the regulations have added to the cost. If you have to tow a lot in a high altitudes and drive a lot of highway miles, then diesel is really your only choice. However, I am going with gas on my next HD truck. I won't need the extra power fue to my driving habits.

They make octane booster so you can buy the cheaper fuel just get a gallon jug of octane additive follow the directions and add it but if you're not too concerned about your warranty you could always put a procharger on that 6.6 and especially since you're that far above sea level it makes sense

JB, as a diesel owner (97 f350) I would not buy another diesel truck.the truth is that it's hard to find diesel mechanics/ shops etc, and due to the amounts of restrictions on diesels vehicles their getting bit unreliable so most people are scared. Atleast for me if I have a gas truck and I am traveling from east to west and I broke down I could find hundreds of mechanics shops and maybe be on the road faster then having a newer diesel trucks. Then again that's just my opinion 🤷🏽

We sold our 2007 , 2500 gmc sierra diesel truck with 15000 miles and bought a 2500 Chevy gas Ltd truck because I found that my diesel truck I had replaced the same sensor 5 times and it was not reliable to drive and not break down in the middle of the country. The Sierra diesel truck had too many emissions parts that cause it to stop running and cause lots of other issues, became unreliable.

My experience is Diesel have more repairs as they age more maintenance cost more in repairs depending on how you use the truck the gas hand's down is a better option in cost

I really like your channel. Keep up the good work

Dang Utah Gas prices are higher than Diesel. Our gas prices here in the south are floating around the $3.00 mark for Regular. The diesel for a while now has been higher than gas for us here, as to why I'm leaning to get a 2024 GMC 2500HD Gasser. I don't tow heavy stuff at all. I may one day have a enclosed carhauler for my SxS and a place to sleep at night (if I don't rent a cabin). But my only fear is when I head off into the Ozark Mountains that the Gasser is going to hate me. Right now the heaviest thing I would pull is a 20 ft open carhauler trailer with two SxS on it (and newer SxS are getting heavier and heavier each year). My dad currently pulls it with his 2015 F-150 5.0L but it just feels like that isn't enough truck to do that, up in the Ozarks. And we did have a 24' enclosed trailer that hauled two SxS, but back then my dad had a 2013 RAM 2500 HD diesel. It pulled it like nothing was back there, but we hardly ever used the trailer or the truck, except on every other weekend, so that was costly for it just to sit there. So he sold both and got the open trailer we use now. I currently have a 2002 Ford F-150 5.4L and it's on it's last breathe I think. I will be keeping my truck for a long time, since I have had this F-150 since 2004. So I'm not too worried about resell value and it will be my daily driver too. So I feel like the GMC Sierra 2500HD 10-speed Gasser is the pick for me, even though I'm not too happy about the MPGs, but that's what you get with a big truck, and the 6.2L in the 1500 doesn't get that much better fuel economy. And you might be asking, why don't you get a GMC Sierra 1500. Because when I have priced them out, the 1500 cost more than the 2500 I have built on the Build and Price configurator. Why pay more for less?

Definitely location specific. Here diesel has been way more expensive than gas for almost 20 years at this point

It's May 11th 2024 on the 15th I'm getting a unicorn delivered. A extended Chevy 2500 Express Cargo van with barn doors and the 6.6 but with an 8-speed automatic transmission. I'm so excited can't wait to get it. Waiting on it I won't get it probably till the 22nd. As it's clear across the country from me. This particular van I've been searching for for months. They just don't make them for some reason. And I know every Chevy dealer I've talked to is upset about that because they sell fast. A lot faster than these pickup trucks and any of their cars do.

here in Upstate NY, Diesel fuel is more expensive than even Premium. Currently 87 octane is $3.25 vs $4.59 for diesel and its over $5 at some places.

This video gave me a good smile today.... 😁😁

I think the filter on the ram you are referring to at 11:30 is a valve cover filter

Another thing to factor in is the resale value. What is the comparison resale value of a HD gas compared to HD diesel? All the 2020-21 2500 HD duramax used still around 90k plus in Canada for 70-80,000 kms

Gas or diesel they can keep the trucks at the prices they want

Stop with the 6.6 gasoline towing a 10,000# or above 5th wheel (you will be very disappointed in higher elevations or where the grade elevation from 3 to 6%). I had an 8.1L 2004 Chevrolet Silverado 2500 HD that could not pull some of the passes in Colorado doing over 35mph. Otherwise the 8.1 performed very well when pulling on the flats or slightly graded inclines. When looking at the diesel engines torque compared to the the torque of the 8.1 it was very obvious that torque makes all the difference when towing in high altitudes or steep grades. I recently purchased a 2022 Chevrolet Silverado 3500 HD 6.6 Diesel with the Allison 10 speed transmission and the towing is incomparable with the 6.6 diesel verses the 8.1L. The 2004 had an 8.1 with a 4:10 rear axil and I was really stuck between the caparison of the 8.1L with the 6.6L L8T gas. Why would I choose a small block over a big block knowing the torque and HP of the 6.6L L8T wouldn't provide the same power and or torque of the 8.1L. To summarize, I tow an 11,000# 5th W with the 6.6 Diesel with a 10 speed Alison transmission, the combination of HP and torque provides sustained towing power on grade elevations that far exceeds what a the 8.1gas engine could produce.

Only thing Allison is that badge 😂

Good information- thanks!

please understand how octane rating works before commenting on it about requirements. 85 octane at high altitude works like 87 octane at sealevel. oxygen drastically effects the burn rate (efficiency) of gasoline. please use google to find actual facts instead of taking the videos opinions at face value.

Thank you for this. Loved it.

Coming in with the videos people want to see! 😎

BRUH ! You do know you can tune a gas truck and change the Cam and valve springs. Cold air intake, MSD Coil packs, wires, headers dual H exhaust BAM ! monster towing vehicle

How much stiffer is 3500 vs 2500

If you are towing heavy or in the mountains then it’s diesel. If you are towing lower than 12K then gas is fine. I’m going diesel all day long.

How is it that diesel fuel is less expensive than gas there? Here on the east coast diesel is about $1 more per gallon than gas!

One of the most misunderstood facts is how octane and elevation relate to each other. If the lowest octane at the pump is 85 then you are at an elevation that your vehicle only makes enough compression to require 85. Every car manual says minimum 87 because 90 % of the people in the world live at an elevation where that is the lowest required. No worries this truck will run just fine on 85 anywhere it's sold. But we are free to pump whatever we think is best. I used to test octane in the highest elevation lab in the US. 7540 ft and 85 would be overly sufficient for this engine from that elevation and up.

Payed 5.29 regular 87 in CA today

I like they quit spelling chevrolet across the grill, that was the only reason i bought the gmc

Sucks when the diesel option is 10k more… I remember in 2015 when I bought my current truck, it wasn’t as near the difference….. like a 6.4 hemi vs 6.7 Cummins

Should I go with a 2500 gas or 3L 1500 high country with tow package ? Max weight towing is 10,000 and that’s for 15km each way at sea level.

I love them both!!!!

I will say after owning a diesel most people today dont need a diesel truck. Diesels are no longer a grocery getter vehicle like you could do pre emissions stuff. 95 percent of diesels i run into don haul or tow anything. And im sure the amount of hauling people do they couls get away with a gas engine for alittle bit. Also with the the added emissions stuff that you cant delete without worrying abt being fined that stuff has made it cost effective enough to not own a diesel. Also dont forget added cost on maintance on a diesel. I love diesels just not the government mandated emissions diesels.

I would go gas 6.6

Good comparison info. Baught diesel....hope i run it hard. Will keep watching u.

driving my 5.7L vortec up to 10,000 ft you could certainly feel the power loss and I oculd only maintain 50mph on the highway without a load. My duramax has zero difference going from 6,000 to 12,000 ft driving. its illigal in the US to void warranty with modifications but it does cause potential contention if the dealer blames the modification for your particular failure you run into.

Allison branded….. not a Alison 😊

The payload is what's important. Then he says the diesel has less load but has so much more power so thats what's important. Long story short this guy is taking out of his ass.

The better but is the one that is more reliable wether it’s a 6 speed or 10 speed. I’d prefer reliability over gas savings. My 2020 Ram 2500 6.4 gas gives me about the same mpg’s as it’s competitors but yet I have that stupid cylinder deactivation. With that bs the Ram should give us like 25 mpg’s to have such a unreliable unit. If nit take that MDS off. I did not know my truck had that otherwise I won’t of bought it.

Diesel buyers buy trucks for the mileage, power and torque and longevity! If you have to worry about gas prices you can't afford a diesel truck!

Anyone have a sense of the difference in MPG between the GAs and Diesel?

beautiful truck

Diesel just sounds better. Pay 10k for sound.

I Have had both and will never buy or Own another Diesel truck EVER !

Which is faster

The transmission is not a gamechanger if your towing daily. I have a 2024 2500 Duramax with the midnight package. never going back to gas!

85 combastibility in high altitude is the same as 87 = you are still within specs to put 85 in high altitude. putting 88 in high altitude is the same as putting 91 premium - waste of money because the engine will need to adjust to detonation ahead of optimal compression...

Gas is always cheaper to buy and upkeep in the east diesel is 1.50 higher a gallon gas wins all the time

Do GMs have bad transmissions usually? Or why the whole Allison advertisement? You don’t hear Toyota saying “brand” transmission.

I can go with the L5P Duramax.

Gas engine is more than enough for most people. I see so many new diesel rolling around town with no cargo, no trailer, and one older guy driving it. Absolute waste of a vehicle.

Your gas is a dollar more than the southeast. Also, diesel doesn’t rev as fast and doesn’t get as hot as gas engine.

Hey bro you don't have to reply to idiots. Love the videos. Maybe we should have beef videos, that would create a lot of controversy like an east coast west coast battle off

Not an Allison it is a Ford 10 speed that Gm developers with Ford

I dont see how he could possibly deduce anything that he is stating without having actually bought, driven, and towed with the vehicles he is toting on-paper facts about. Watch actual useful channels that USE these trucks, not some guy standing beside them

but gas prices for diesels, diesel fuel cost more so you save nothing.

Diesel all day long for me.

Diesels cheaper ! Nice 😎

Damn, diesel is cheap there! Here its still 50 cents higher than high grade gas

They don’t have a Allison built 10 speed! Branded only!! More GM lies!😢😢

I doubt the 400k miles out of a modern diesel

Isn't that less power than a 1/2 ton with a 6.2 L? 420 hp & 460 pf torque.

SLC 4500' above sea level

Allison has nothing to do with the 10 speed.

Great video! I was to chicken to buy a new Chevrolet truck two months ago and went with a 2023 Nissan pro4X XD. my 2016 camaro 2ss and GMC Yukon just left me with a bad taste. Sorry GENERAL MOTORS. My dad probably rolling in his grave that I steered away from GM.

Not power, but pulling torque, horse power belongs to gas.

The front end styling is much better than before but still not very good. These have a very praying mantis looking front end now. There are still other styling issues as well concerning the roof structure, top of the front door frames, mirrors, rockers, etc. GM is still using the useless wax covering for their frames too.

My 87 octane is $3.04 a gallon, glad I don't live there

Could you do a mpg video like a 100 mile loop on 91 octane vs 88 e free