Fwd pressure drop and hard engagement sounds like you cut a seal in the forward clutch or the sealing rings have worn a groove the drum. When this trans shifts from 3 to 4 the fwd clutches come off and the o/d band comes on. If your not getting a lock up on the upshift then the forwards must be coming off. If you get a lock up on the downshift then the forward clutch is coming on before the band comes off. If you suspect a worn servo bore then go to a small servo piston with sleeve. Also update the accumulators to molded design. What happens when your in o/d and hit the o/d button. Does it go into 3rd without bind up?