On my 91, I had a similar problem. I wasn't able to shift into 2, 4, or reverse. My first thought was that my trans was blown. I took it to a trans shop and it turned out that a bracket attached to the trans had broken and was blocking the shifter. Unfortunately, it was so long ago that I don't remember the details of said bracket. i wish i could give you more info, but maybe this will help.
-David