That job is probably best done with the rear end housing out of the truck and on a couple of saw horses or a big workbench. If you put too much down pressure on the torque tube you might bend it, and at best, you're working in very cramped quarters. At the very least, remove the U bolts and slide the whole housing back a few inches on the springs so the front end of the tube can be manipulated without trying to bend the spring leaves.
Jerry