After sitting for several years, on top of being a 15 year old vehicle, besides changing all of the fluids (fr and rr diffs, transfer case, brake fluid, coolant, ATF and power steering fluid), and dealing with whatever rust is underneath I would also consider replacing all of the rubber parts because they break down faster from lack of use:
- accessory drive belt
- PCV
- Rear Axle breather
- Radiator hoses
- gas cap
- pressure test the radiator cap to confirm it is still holding 15psi for at least 15 min.
- check the age of the tires
- consider changing the 6 rubber flex brake lines