That's a good weekend job to do, just make sure you buy correct gear lube for your rear diff. should be in owners manual or possibly switch to a synthetic lube.
Here's a little guide to see and read on how to do, its a Gm truck in guide, Chevy owner here, but shouldn't be no different--------
LINK
With only 36K on your truck, it wouldn't be necessary to remove diff cover, drain plug would be fine, if your diff has a plug that is, but that choice is yours.
Good Luck and have some fun.