4l60e 1-2 shift does not happen at WOT

[JNJchev77]

..... until you let off the gas! Trans was rebuilt and only has about 300 miles on it.

I have a ported throttle body, CAI, Cam/Springs, and basically a "stock tune" I guess you could call it, from PSI. Also put a corvette servo in for shift firmness...
3.08 rear end, but computer is set up for 3:73 as I will be changing gears. Was told this wouldn't cause any issue with anything other than Speedo...

Would a tune help? Could this be a TPS issue? All other gears seem to shift fine and when I'm at about 1/2 throttle, 1-2 shift seems fine... I know very little about transmissions and have been researching and retaining what doesn't go over my head lol...

Thanks,
Justin