4l60e shift issues after engine and converter swap

Build: 99 Silverado 5.3,218/227 cam, ported heads, ported throttle body, LT's, 2000 stall, and Stage 1 Performabuilt Trans (installed when trans went out before
engine build).

Problem: Transmission shifts fine under light acceleration, but when rolling into the throttle or trying to accelerate hard it acts like its trying to flash stall between shifts. If I get up to cruising speed and roll into the throttle it downshifts correctly. Then pulls hard until it gets to the upshift again.

The trans shifted fine before I did the motor and converter. Can I make adjustments with HPT that will correct my issues. I'm still working on the motor tune and felt it easier to ask than to search the threads. Thank You for any help you can give.

This sounds like an engine tuning issue.
Please post this in the GM V8 Tuning - Engine, Gas (Gen 3) forum, and include your current tune and logs if possible.