Mrplease & drol.

The clips in the shock bag are the travel limiters. You need 3 to 4 of those under the black rubber bumpers that are on the base of the shock shaft to limit up travel.

Without the limiting clips your suspension is allowed to travel too far causing the a arm and the cvd to make contact with the outdrive. That pushes the outdrive upwards and cones the shim under the sun gear loosening the gear mesh and then you get clicking or stripping of the diff gears.

A rear rebuild with a new set of gears is probably in order at this point, maybe while your in there a new diff case as well.
New shims under the sun gear (2 big gears in the diff).

Push the suspension ALL the way up, not just push the truck down to the table... all the way up. See the a arm and cvd getting into the outdrive?

This needs to become it's own thread so it's easier to find, many people have this same problem.