Unless he received records indicating the last fluid changes, I would replace the engine oil and oil filter, air filter, fuel filter, transmission fluid and differential.
You might also consider bleeding the brake fluid (especially if the fluid is dark in the reservoir) as well as repack the front wheel bearings. Cheaper than getting caught on the road with a bad wheel bearing. At that time, you can inspect the front pads and rotors (use Performance Friction pads or Napa which have a lifetime warranty).
2WD dually front rotors are fairly expensive. $200 / each because they are integral to the hub unlike the 4X4 version.
Then there's the engine coolant. Flush and refill.
Good luck.
Redram