They are great trucks, but the tranny can be an issue. If it'* given regular filter changes and filled with the CORRECT Mopar fluid (not that Dexron/Mercron crap, not "mopar compatible" either, but REAL Mopar fluid) than they are just as reliable as anything else. Luckily rebuilds for the 904 are easy and cheap.
I'm assuming it'* a Magnum 318. They are a pretty good motor, there are certainly many options out there as far as building it up.
Suspension Techniques has a good drop kit, and www.polybushings.com
has a great set of motor mounts.