Bought a Performabuilt stage 2 with stall, along with a cam kit, computer tune etc.. After the install I had no 4th gear. No slipping in other gears, and drives fine in 1, 2, and 3. When I should be in od it just doesn't shift, and when I let off it drops to an idle and rolls.. I am forced to run everywhere in 3 to keep the fluid flowing.

The transmission itself is fine. Performabuilt AND local shop looked at it. The local trans shop manually shifted it to 4th. However when attempted on its on, live computer diags showed a command to shift to 1 when it needed to go to 4.

The only other thing I thought would seem likely is the computer tune from Trifecta. Contacted vince. He looked up my tune and said it wasn't my problem.

I am stumped and its unfortunate bc I have maybe 6 months left on my 2 year transmission warranty, and have not even 500 miles on it. Any ideas would be appreciated. Thanks

 

What are you using for scanning or logging ? Can you see the 'Encode Shift A & B ' status indicators to determine the PCM shift commands to the transmission. 11=1st, 01=2nd, 00=3rd and 10=4th. You should see RPM drop about 250 Ms (1/4 second) after up-shift commands if all is working. Also are you seeing any DTC 37 brake switch stuck on, DTC 38 brake sw stuck off, or DTC 90 TCC circuit. Any of those will block 4 th gear w/o lighting the SES indicator.. What software, if any, are you using ?

 

I didn't find the shift commands, the local transmission shop did. That's where they said it wasn't the trans, and they couldn't help me.