4l60e trans questions.....help!!

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in the past year my car has been getting dialed in more and more....receltly i installed a carbon fiber drive shaft and man the car feels phenomenal !!!!!!! revs up faster and feels like more power... the problem i have now is with my 4l60 is my first to second shift is good although inconsistant at times, but my 2-3 under wot wont shift!!! i will only shift if i lift and let it shift. i believe my 3-4 is the same way. my trans controller is a psc unit and after dataloging it and sending it to them they say the controller is sending the signal to shift, however it doesnt. under normal conditions the trans shifts perfect! Psc says i might be over powering my convertor..any ideas?

thanks Pete