Rebuilt 2001 Camaro Z 28 using Jasper Rebuilt unit. Under hard launch the Transmision slips after engagement into second gear and after into third gear the transmission surges as if I press and release the accelerator. Took car to a local reputable transmission shop in Houston and had the internals upgraded with new parts that are used for racing as the engine is producing 425 rwbhp. Got the car out of the shop after a $2710 repair. Took it out yesterday and the same issues remain. Could this be a tuning issue or a tranny issue?

 

I certainly don't know the answer, but since no one else has replied, no one else is sure either. It sounds nearly impossible to diagnose this without logging many trans and engine parameters.
If you assume the trans was properly rebuilt, I would first look at the critical engine sensors like the MAP, MAF, TPS and VSS. Sure it could be a crazy tune, but you really need to log the trans and engine parameters to debug it. Just my opinion; perhaps more experience people have better ideas.