Fresh 904 race trans, 2nd to 3rd shift issue

When at the track under full power, second to third shift feels like it actually drags the engine down, almost like it bucks a second before the shift is completed.
Has TA Reverse man valve body, putting around on the street seems fine, don’t notice anything, first to second shift at track seems fine too.
my builder swapped out an A&A brake I never used for this TA valvebody during the freshen. Has 5.0 band lever if that matters.