BTW, the owner's manual says to never jack at the differential. It's unsafe to do that. You need one tire on the ground with the parking brake locked even if you are using tire chocks (which I do).
Yeah that's mostly a liability/protecting against lack of common sense type thing. If you're on flat ground, you can jack under the diff and not even chock the front wheels. While you should chock the fronts, It would take some serious force to get the truck rolling anywhere with half the weight of the truck on the jack wheels to try and roll, and once you get the jack stands under the rear axle, it's not rolling anywhere.