help!!!!!

I have a 2001 eclipse gt and I think the auto. transmission is going out. When the car shifts from 2nd to 3rd it drops to 1st to get to third and when it shifts from 3rd to forth it drops to 2nd to get to forth. I can not find a used trans anywhere. Is there other cars that have the same transmission? I heard some where that the galand v6 trans would work. Any help at all would be great thanks in advance.