Hi Mike,
Here's what I would do
1) check cap, is it tight? If yes, remove and top off w/ water
2) drive the truck for a short test drive, does it get hot (temp gauge may not be accurate, but if you pop the hood after the test drive and it's hot you will hear it boiling-DO NOT open any caps or hose at this point)
3) If not boiling or hot, do you have any leaking right after test drive from hoses, engine, radiator?
4) If it is boiling, time to troubleshoot what you need I suggest top off fluid, spray out radiator w/ pressure washer if debris is clogging it, thermostat, fan clutch. Very rarely does a guy need to replace the radiator or even have bad fluid, but a flush isn't a bad thing if your vehicle is 18 years old. Fan clutch has been the answer for me in a few ocassions, especially if you see it spike temps on hill climbs or in the city driving with a/c on.
