Make sure you can pull the fill plug before you drain the tcase. Tranny fill plug is on the dside of the tranny, about half way up. I use a drill driven pump that hooks to garden hose and a single washer hose cut in half for two threaded hose ends, and a J bent piece of copper tube hose clamped to the washer hose for a filler.

85-90w gear oil is fine for the tranny and tcase. I have had serious recommendations from tranny pros to use atf in the gearbox, and I know of one with nearly 200k miles with nothing but atf used inside. If you have an lsd in the rear, you need lsd gear oil additive along with the gear oil, or the truck will shudder in tight turns as the lsd clutches chatter, and you'll get extra lsd clutch wear.