El Conquistador is right. You have a Mazda-designed M5OD R1. It's a lightweight transmission. Two common problems are (1) bent shift forks, and (2) broken plastic bushing in the shifter. The plastic bushing is a DIY job. Pull shifter boot, pull a few bolts out that hold the shifter in, pull shifter, replace plastic bushing, reverse procedure. Bent shift forks require dissassembling the transmission.

Read up on the Mazda tranny in the 87-96 F-series forums (a different version, the R2, was used behind 300 and 302 motors), and in the tranny forum.

You might just get your transmission rebuilt if you have anything close to 100K on it. That seems to be about the practical limit for an M5OD, from what I've seen.