Kelly Blue Book is your best friend. Check the seals around the oil pan and axles. Check the front U joints. Make sure all wiring is got the factory shielding on it and it hasn't been tampered with. Ask about service history. Driving it and check and see how tight the front end still is. Listen to the engine as it idles and when your drive it. Don't be afraid to get into it a little. Make sure the transfer case shifts and goes into high 4WD and low 4WD. Check the antifreeze and see if it's using any.
Other than that wheel and deal man and don't be a friend to walk.