99 Cadillac STS won't shift at redline...what's wrong?

1999 Cadillac Seville STS, w/ the 4.6L V8 Northstar motor & 4T80-E trans. The engine and trans were out for lower crankcase oil seal replacement. Everything went back in and the car runs great. The only problem is that (in any gear) if you hit the gas pedal and keep it on the floor, it'll first downshift... show more 1999 Cadillac Seville STS, w/ the 4.6L V8 Northstar motor & 4T80-E trans.

The engine and trans were out for lower crankcase oil seal replacement. Everything went back in and the car runs great. The only problem is that (in any gear) if you hit the gas pedal and keep it on the floor, it'll first downshift into "passing gear" but then as it reaches the redline (6500) it doesn't shift, just keeps going into the red.
If I release the gas pedal near redline just a touch, it'll shift into the next gear and all's good.

Before, it always shifted at the redline. The trans shifts normally in every other kind of driving and it's all smooth, it goes into all the different gears when it's supposed to. It's only when you floor it and keep it floored that it won't shift at the redline.

I've checked for codes (I can access everything, ABS, transmission, airbag, etc. not just PCM) and there are none. The car runs perfectly otherwise and the trans fluid is at the right level.

Please help!
Update: Well, I think I've KINDA figured this out. I don't think there's anything wrong, anymore...but I still can't explain the change. I was looking at the tach today and realised it used to shift at 6250, actually, not 6500. I decided not to worry about the red area on the tach and to just let the... show more Well, I think I've KINDA figured this out. I don't think there's anything wrong, anymore...but I still can't explain the change.

I was looking at the tach today and realised it used to shift at 6250, actually, not 6500. I decided not to worry about the red area on the tach and to just let the computer worry about protecting the engine, did a full throttle acceleration and sure enough, at 6700 or so it shifted without any drama. Did it again and same thing. So, I think it's actually shifting at around 6500 now but I'm just seeing the needle swing past. With no codes and a proper shift (no fuel cut out, so it can't be hitting the rev limiter at 6800), I think it's fine. The only thing I can think of is that the ECM was reset when the engine/trans was out and is now shifting how it should...maybe before someone really babied it and it lowered the shift point for WOT? Who knows.

Thanks for everyone's input on this.
4 answers 4