turbo 350 tranny trouble

I just put a used turbo 350 tranny in my truck, t was supposed to be good. Reverse is really strong but it slips in the forward gears. Looks like there are 2 bolts to turn to adjust on the passenger side of the tranny. Is there a way to tighten the belt for the forward gears. It also sorta feels like there is a brake on in the forward gears. Is there any help for the transmission or is it a dud?