Transmission want shift after gear swap

Dewayne Mosley · January 9, 2020

I have a 2011 chevy avalanche and recently swapped out my 308 gears and installed 373 gears. Now my transmission will not shift out of first. My truck pulls about 10 feet and quits pulling. I can manually shift it and it has all 6 gears.

sefiroxx · January 9, 2020

2wd or 4wd?

Have you pulled codes?

Dewayne Mosley · January 9, 2020

There are no codes. I had the truck tuned a while back and the only code was a map sensor in which I have replaced. Had a couple guys that said it was the TCM due to being able to shift it out manually. Just had it replaced and programmed, same thing

Dewayne Mosley · January 9, 2020

Was shifting perfect. Pulled 308 gears out and installed 373 gears. Went for a test drive and put the truck in "Drive". Truck pulls about ten feet and its like it goes to neutral. Pull in down in manual and can shift it out through all 6 gears.

It's Tim · January 9, 2020

53 minutes ago, Dewayne Mosley said:

Was shifting perfect. Pulled 308 gears out and installed 373 gears. Went for a test drive and put the truck in "Drive". Truck pulls about ten feet and its like it goes to neutral. Pull in down in manual and can shift it out through all 6 gears.

Are the bushings intact on the shifter cable?

Dewayne Mosley · January 9, 2020

Yes

Grumpy Bear · January 9, 2020

Did you tell the computer about the gear change?

riverbanks · January 9, 2020

Google,fast learn for your tranny

Dewayne Mosley · January 9, 2020

Yes. ECM and TCM both programmed for the 373 gears

Korbin · January 13, 2020

That’s super wack I’ve never heard of this before and would have no idea were to even start good luck with this one

Gagliano7 · January 14, 2020

It has to be a programming problem. Who ever tuned it missed something.

Dewayne Mosley · January 16, 2020

Had it retuned and no difference. The carrier in the old rearend broke upon taking off. Some locals are saying I may have bent or broken a sprag in the transmission????? Anyone here familiar with this?

davester · January 16, 2020

Well, it makes more sense now. You were giving it the beans, and broke the rear diff. That's totally different from "recently swapped out my 308 gears and installed 373 gears"... Your transmission could easily have been damaged at the same time.