I'm with 4x4grey88. My '88 had a similar problem. Funky shifting, "hunting" between 3rd and 4th, and it didn't downshift when I punched the throttle. Two places told me I needed a new/rebuilt tranny. Turned out it was my TPS too.
Broken mounts seem a bit odd for your vehicle unless it's seen some hard 4 wheelin'. But then both motor mounts on mine were broken.
. What a difference changing those made!