Change the rear diff gear oil. The rear diff is in use full time. It needs new oil.
Change the transmission oil. Same reason as above.
Check the front diff oil. Doesn't need replacing as often, but if it's sludgy, you'll need to rebuild the steering knuckles. Sorry, but it's one of those things every owner puts off. And now you own it. You can put it off too, but you should at least find out where you stand.
(I put it off for a couple of years. Finally got around to it after sweating through a couple months of death wobble. YMMV)
ps - Welcome to mud
