ShowstoppaTransAm

I have a 2001 Trans Am 174,000 miles. I just had new axels and 373 gears installed. I had the tranny rebuilt. Reprogramed speedo with a Hypertech programmer. If i'm traveling at 60MPH / 2,000RPM here's my issue. If i go over a hill and hold speed (60MPH with or without cruise) when i get to the bottom of the hill (car kinda coast downhill) and give it gas to maintain speed (60MPH) the RMP shoots up to 4,000RPM but the car doesn't accelerate. The car want shift right until i stop and take back off. It doesn't do it everytime and want hardly ever do it on flat land. The car has NO CODES. It want never do it when the transmission guy takes it for a test ride. It did it one time and I floored it and held it for a minute and killed my transmission. My car wouldn't drive over 20MPH. That's why it was rebuilt. A new TQ was installed also. He didn't replace the shift selonoids. Could this be it?

ANY AND ALL ADVICE WILL BE GREATLY APPRECIATED

THANKS

ShowstoppaTransAm

I had some new shift solenoids installed but it didn't help.

Somebody has to have some idea what's wrong.