tune up

What items should I replace on my 99 ranger 4.0L for a complete tune-up? I recently put in a new fuel filter and Bosch spark plugs.

I have the same type/year Ranger. With the advent of electronic ignition and emission control, there's not much that involves what used to be called a "minor" or "major" tune up. The requirement generally involves a lot of "checks" and "inspects" Even the plugs don't have to be replaced until the 75-100K mile marker. Of course the fuel and air filters need changing every 15K miles and of course I change my oil every 5k miles. I recommend you check the maintenance schedule booklet which came with the veheicle. A good visual inspection of engine components done periodically is highly beneficial. I also add a good fuel injector cleaner to my gas tank every couple thousand miles.