I supported the rear control arms and disconnected the shocks, sway bar links, and even the pivot bolt and dropped the springs, carefully!. Then support the differential in the center on a jack, remove the 4 bolts that attach the subframe, and gradually carefully lower the whole rear diff/subframe assembly about 4 inches.
Did you use one floor jack in all? In other words you went around with a floor jack and used it at each corner, supported the different parts and then used it to finally lower the differential?
I am considering do this, that is why I am being specific. I have four jackstands and a very good floor jack.