727 issue i think?

abbreviated story. car sat for a year with the engine apart getting heads ported new cam and all new interior.

now running again and when under power shifts great. when just being easy on the throttle and shift from first to second goes perfect, if i stay in second just easing on the throttle it will begin to for a lack of a better explanation feel like i am applying the brakes. shift into third and it frees up and back to normal? what the heck is going on? normally i never cruise in second for any extended period of time but this doesn't seem right to me.

trans specs. 727, redline clutches and bands, bolt in sprag, cheetah reverse manual valve body, 3500 stall turbo action converter. engine 416, rear 8 3/4 3.91 gear.