Newbie here, but long time lurker. ;D I have a friend with a '96 Impala SS (LT1/5. 7L) that I rebuilt the transmission in. He races this car pretty often. It actually has a stroked LT1 in it (with cam, heads, headers, etc. ). His old trans was trashed; clutches were shot, apply piston seals were blown, shell collar was broken off, etc. We built the trans with the new beast shell, kevlar band, shift reprogramming kit, corvette servo, hd clutches, and a few other upgrades. It also has a new 3200rpm stall convertor. The transmission shifts fine under normal driving except that it shifts from 1-2 a little too soon. But of more concern is that at wide open throttle it won't shift from 2-3rd at all. He carries it to about 6500rpms and then lets off. I had a trans pressure gauge but I loaned it out and it never found it's way back home. So, this morning I just ordered a new one from ebay. My point being that I haven't checked the lines pressures yet. His ECM has also had some custom work done to it and he has an appointment next week to have it dyno tuned. I'm curious as to what I should look for that would cause these problems? I know that normally the 3rd clutches would be of concern but they're all new along with pretty much everything in the trans. Could it be something in the ECM causing this? Thanks for any help!