Here to pick some brains because my friend who has been doing all the warranty repairs is stumped just as well as I am.
Here's what I've got. I've got an 08 grand prix, bought it to replace my impala 3800 with a ton of miles on it, it had 22000 miles on it when I bought it and now just has over 30000 on it now and since I've boughten I've noticed going up and down hills, west central Wisconsin we've got a ton of hills, it has a steady jerk going uphill before downshifting. As it downshifts it takes of normal, but before downshifting rpms will hop up to 500 rpm. GM has reprograomed the shift points. No luck. Replaced a wiring harness and a lever. No luck. New valve body, all new fluid, and new filter, no luck. Cleaned throttle body. Same thing. I am a mechanic at a smaller shop my grandfather owned for 50 years and now may father has taken over and we've looked at warranty not a lot due to it being under warranty. I've analysed scan tool data....no misfire, no maf jumping around, no tcc on off on off. Steady. It does seem worse when wet too. I'm not sure if its any relation. I'm kind of at ends with this thing. Wanted it for the last making of the 3800 engine and now wish I kept the impala. I don't think its nothing major. I Just think were over shooting the problem.
If anybody has a guess I'm willing to try it. Idles great runs great except for uphill on a load.
Thanks!!!
