like your video and if you take one more could you concentrate on the speedometer and gas pedal because i could compare it with mine. my transmission works like yours. I have the 455 ( a gorgeous machine) and going up the hill i personally place it in S or press the accelerator to 3/4 to maintain 40 -45 mph. then i hear the secondary carburetor barrels opening because of the change of noise ( like a roaring). temp never goes near 3/4 of temp dial with a/c running. those engine needs rpm to develop enough power to move the 12,000-pound mastodonte beast. you vacuum modulator appears to be in working order with the downshifting when the engine was looking for a breather. sometimes i wich i could have another 100 horses. some other owners climbing a very incline press the pedal to the floor and they keep it there when they are climbing 3,000 feet in 20 minutes.. they work like a pumpkin you push it uphill and then let it roll downhill. oc@@babyboomersrvs3834
Why do you reckon GMC downsized from a 455 cu. in. (7.5 litres) V8 to a 403 cu. in. (6.6 litre) V8 engine? I would think the smaller engine would be fine for a smaller (23' or 7.0 metre) GMC Motorhome, but you'd need the much larger engine for the larger Motorhome.
For a vehicle of this size, I don't think a 6.6 gas engine would be enough. I'd want mine to have the much larger engine. *Maybe* if it was a 6.6 litre Duramax Diesel or some other V8 Turbo Diesel engine.
