The in-line fuel filter shoud be replace every 30-35,000. The plugs I would do every 50-60,000. Air filter about every 15,000, but check it first. Kinda buried. Might just wat to replace rather than screw around, Get a look at the pcv hoses and valve as the hoeses tend to collapse. Clean the throttle plates and intake valve every 20,000.
I would also suggest a transmission filter with the right fluid every 20,000 on these trucks and coolant flush every 2 years.