if it is a stuck valve in the valve body from tarnish buildup, there is a additive you can buy called lube gard
http://www.transmissioncenter.net/lubegard.htm ive used this before and its pretty good stuff you can get it at most NAPA stores. you can also try some stuff at NAPA called sea foam that works good too. if these dont work for ya id be lookin for a good tranny shop...later