AOD trans slips in od

i recently got a 90 gt, former tranny blew up, i got the car with a used aod from a crown vic i installed, it worked fine after dialing in the TV, but slipped in OD when you hit the throttle. i had to feather it while in od, or manually downshift. now after spending 5 months in my garage getting a full body makeover, it slips as soon as you hit the gas. i tried readjusting the throttle valve, but it shifts too soon in 1st, 2nd and 3rd, and just barely holds in od. it shifts ok in 1,2,and 3, a little on the soft side, but its ok. would a shift kit help this at all, or are the bands or clutches in od just gone?  any help is greatly appreciated!