bts17

I'm no expert so some help would be much appreciated. I'm having serious issues with my rig, 22re engine seems to be running as normal in neutral: very smooth and good power. My truck is driving rough.. especially when i hold the tach at 2200 in 4th gear around 40-45mph. When in gear and power is going to the wheels the whole truck shakes very hard and vibrations run through the truck. Sounds like the truck is missing, or tranny issue. I found the rear tranny mount and the rubber mold on one side is completely seperated. Could this be the problem? I changed the transmission fluid and tuned up the engine(wires, plug, distributor cap). I'm also leaking out the rear engine seal like crazy all of the sudden. Any ideas?
-1992=22re, 5 spd, 4x4