We have a 07 avalanche 4x4. The transmission was just rebuilt and installed. When you take off it shifts 1-2 fine. When you get to like 22mph it seems to shift back to 1st and the speedometer starts dropping until it gets to zero. The vehicle isnt slowing down when speedometer drops. If you come to a stop it repeats the same process all over. We have changed the vss and it did not fix it. Looking for ideas or suggestions on wheat to check next. It will shift to third if under 22 mph.

 

The 3-4 Clutch is not Applying.

Inspect the External Wiring, Internal Harness and Solenoids...

The abnormal Speedo behavior in addition to the Failure to Shift Up to 3rd-Gear would direct me to look for an Electrical issue First.


You should try and get a hold of a Scan Tool or Software that can Read Transmission and Body DTCs for Open/ Alter. Circuits.

 

Hmm is it was a 4L80E I would think the speed sensors were swapped but a 60e and a 4x4 and the speedo dropping to 0 hmm strange.

 

The front prop shaft and the vss sensor plug was swapped.

 

I was close on two plugs swapped, Just didn't realize those two would swap. Good to know for future reference.

 

Both prop shaft and the vss are within about 6 inches of one another. We tore this thing apart almost three years ago,so we didnt remember ourselves.