I know what it is and yes, more then likely it is your TPS. Just take it back apart and you should find what's wrong.
What's happening is that the TPS cannot correctly detect half to wide-open throttle. Moving the throttle directly to one of these positions, will induce a downshift from the transmisson. Since this is not happening and we know that the only thing that has changed on the car is the TPS, it has to be the problem.
The TPS is not something that can just be thrown together. Not harping on ya, just stating a fact.
Take it back apart and rotate the internals more towards the ground. This should bring everything back into check. I'm not exactly sure how you do this, but I know there have been several people on here that have modified their TPS and had the same problem. And almost everytime, they had it or the internals miss positioned.
