if its reving higher before changing its possiblely the clutch band not holding the drum for it to change, if so thats a reasonablely quick and cheap fix since a clutch band is only around 30 bucks and its behind the pump at the front of the tranny so you dont have to tear the whole tranny down. i would drain the fluid and check to see if there is any friction material in it. thatd be something you can do in your drive way and atleast get a idea of where to look