Engine Revs up and down at 35 to 40 mph

[Mudsport96]

If it turns out it's just doing what the (GM OE) program is telling it to do, the solutions are:
Use Tow / Haul mode to avoid this behavior - assuming this might work
Have pcm properly reprogrammed - this WILL DEFINITELY ABSOLUTELY POSITIVELY work if the gripe is thoroughly understood by tuner

I can look at the program again after work tomorrow, but usually the tow/haul bumps the 2>3 shift pretty high. So it may not even be in 3rd by that time. I always reserve the right to be wrong without checking to be sure though. Lol

 

[Mudsport96]

So if you throttle position in 4th gear is 30 percent to 35 percent between 32 and 48 mph it will kick down from 4th to 3rd so that could be it

And I don't think leaving it in tow haul will help, as the 2>3 shift doesn't happen in tow haul until 36mph at moderate throttle. So that will cause it to Rev pretty high. And the converter won't lock till almost 60mph.

 

[Mudsport96]

Also just found this file is for a vehicle with 3.73 gears. So if you have something other, it could be a few mph either way.

 

[mattbta]

TunerPro is fun. Also universalpatcher.

 

[Alaxgoaly8]

If it turns out it's just doing what the (GM OE) program is telling it to do, the solutions are:
Use Tow / Haul mode to avoid this behavior - assuming this might work
Have pcm properly reprogrammed - this WILL DEFINITELY ABSOLUTELY POSITIVELY work if the gripe is thoroughly understood by tuner

I tried tow/haul mode and using 3 instead of D... While I didn't see the exact scenario, it was similar. I'm going to try both again to try and recreate the scenarios again.

One thing I haven't looked at is the exhaust manifold bolts. If the bolts are loose or missing or broken, would the problem get worse as the engine is warm? The engine and trans do not overheat. I'm wondering if once the engine gets to temp, the exhaust manifold expands and the leaks get worse and causing misfires to get worse. Which could be why the transmission specialist saw nothing wrong with the trans data but saw misfires, but my normal mechanic said it felt like a trans slip? Does this hold water?