New Plug Wires, Driving North & Transmission Problems 

Awesome thanks for the info, that helps alot! When it was supposed to be in 4th, and I let off the gas, it would just coast and rpms would drop to idle like it was in neutral but third would re-engage when I hit the gas to speed up.. Does that help tell you anything more about what's going on?

@@ClassALiving Hmmmmmmm. That's unusual. Not sure about that symptom. If you get time, check RU-vid for posts about your transmission and troubleshooting it. I think yours is the 4L80E, or the 4L60E. It should have an Identification tag on the side that will for sure tell you which one it is. The "E" stands for electronic controlled, by the ECM. Something else; make sure to check all the wiring harness plug-ins at the trans, and at the ECM itself. Check them for any signs of corrosion or poor connections, looseness, or damaged wires. Had a 1996 Silverado 1500 with the 4L60E. It was giving me fits with weird shifts, skipped shifts, etc. The problem turned out to be corroded terminals at my ECM connectors, caused by a leaky windshield weather seal. Pulled, cleaned, lubed with dielectric grease all of those pinned connections....problem solved!!! Good luck finding the issue!! On another note; I'm so fricken pissed off tonight after what they did to our man, Trump. Makes me so damned mad. If we don't stand up now, and do something, we are going to be in deep doo doo.

Nice that you try to help.

@@ClassALiving IIRC with that era of gm computer control strategy, once overdrive is engaged and you let off the accelerator, the system should do what it is doing now, ie rpm drops to idle during coast but downshifts to 3rd to re-accelerate. you might have a slipping tourque converter clutch.

Hope you can figure it out. I would check it out some more like others mentioned and then price a rebuild shop. They do the work to swap it as part of the rebuild cost most times and if not can pull it from below without more than what you have there already. Some wood blocks on the ground are helpful to get it positioned without a fancy jack and use your normal jack with a wood block to protect the pan. A pain for sure but doable.

And a cheap try, I agree, fluid and filter next.

Glad to hear it! I mostly use craigslist but FB marketplace has been pretty handy in the past as well. Thanks, you too :)

Sweet, I'll have to go see if i can can find one, thx for the tip! To pull the engine, it looks like it would be more difficult to get the the transmission off and a new one mounted with the engine in place.. but idk maybe I should take a better look, pulling the engine could open up a whole can of worms :/

Jack up the truck drop from the bottom. Did it on 95 7.3 diesel. E40d auto. A small floor jack and all day. Remove replace. Good luck. You do not need to pull the engine. Drive shaft cross member transfer case, then trans.

There different patches has a 3 speed th400 and rusty has the 4 speed 4l80e. Also 2 wd versus 4wd cases there similar but different.. wouldn’t be a simple swap nor cost effective.