The timing belt needs to be replaced at 90k on the 5VZ-RE (3.4L V6) engine. If he took good care of the truck, that will have been done on time, and the water pump and all "fan belts" would have been done at the same time. Check for replacement of wires, plugs, filters, and oil/filter change intervals. I run my truck all highway, and change the oil and filter every 5k. You should also check records for differential fluid changes (especially if it's a 4x4).
Check
http://www.nhtsa.gov for any recalls that might be relevant to the vehicle, and ask for records that they were performed.
Hope that helps...