Hey DP crew,

I need some serious help with a transmission issue that I have lived with for past 1.5 years.

2002 GMC Sierra 3500, CC, 4x4, dmax & allison. This truck is totally 100% stock with 135k miles.

The issue.. under normal driving & acceleration, the truck shifts hard on upshift going from 2nd to 3rd and from 4th to 5th. On downshift, from 3-2 & 2-1. On downshift, it is so severe that it triggers ABS. With the above being said, under WOT the shifts are actually smooth.

I had a friend clean the valve body but it made no difference. Fluids replaced many times and no excess junk in the fluid. Had it to GM dealer 2x and they cannot determine the problem and want to tear it apart. My thought is that it must be electrical but it is only a guess.

Is there anyone within 3-5 hours of Lexington, Kentucky that would be willing to help me figure out the real problem here. I'm not looking for free help necessarily but I'd rather not hand over thousands to the dealer either.

Thanks in advance for any & all assistance with this, it is killing my back & neck to drive this truck anymore.

Greg

Does anyone have any direction on this? Thanks!

After cleaning up the valve body did you reset the adapts? Sounds like the issue is related to the A solenoid.

I am no expert so this is only a direction. Have you owned the truck since new? Any chance it was chipped? The c3 clutchs are applied in 3rd and 5th your upshifts have that in common. Does it clunk or anything when you put it in reverse?

After cleaning up the valve body did you reset the adapts? Sounds like the issue is related to the A solenoid.

Thanks for your input! Yes, the adapts were reset and didn't seem to help at all. From what I remember, the solenoid you mention wouldn't be that hard to replace with the valvebody out would it? Im really scratching my head on this and it kills my back & neck to drive this truck anymore.

Thanks,
Greg

I am no expert so this is only a direction. Have you owned the truck since new? Any chance it was chipped? The c3 clutchs are applied in 3rd and 5th your upshifts have that in common. Does it clunk or anything when you put it in reverse?

Thanks for your input! The truck had 60k on it when I got it about 5 years ago. I think it was used as a hot shot for that part of its life but I feel safe in saying it has always been stock. There is no slipping of clutches, only extreme, hard shifts. Occasionally there will be a clunk when I put it in reverse, but I can't say it happens everytime. I can say that the hard upshifts from 2-3 & 4-5 happen consistently under normal throttle and never happen under full, hard throttle. Downshifts from 3-2 & 2-1 are also consistenly violent. So hard, it triggers ABS.

Thanks again,
Greg