First thought is broken trac-bar bracket, or worn TB bushing. Check both ends.
Second thought is worn out control arm bushing(s). There's 8 back there.
Third is broken tranny mount.
Fourth is loose pinion nut
Fifth is worn or broken motor mount.
Loose body mount comes to mind, too. You have a 3" body lift? Trash/sell it, and put in a 1" - 1/4" body lift...