When you get right down to it, there may be a variety of things causing the banging from the tranny to the wheel bearings. A little bit of wear from the slip joint, u-joints, ring and pinion, wheel bearings.. all together can contribute to the banging. Grease EVERYTHING. Some have installed a zerk fitting on the slip yoke on the rear drive shaft to keep it well lubed.
Have you tried jacking the rear in the air and moving one of the tires forward and backward to see if you hear or feel any play in the drivetrain. I would do it before considering any transmission possibilities.
