Ram tranny problems

I took it to another tranny guy today and he said something is causing it to go into two gears at once. He said there's a snap ring that fails in the overdrive that may cause this because of a bad accumulator. He's saying about 1200 to rebuild but that includes a new converter. Is it possible to do myself? I do have some knowledge in trannys. I want to to a book on it just to make sure. I need a parts list that I need to order too if possible.