What all does a "tune-up" actually involve?

 

IMO it's a matter of mileage since the last tuneup or from new.
It can involve oil change, fuel filter, engine coolant, spark plugs, oxygen sensors, air filter and anything incedential to the truck.
With consideration to fault codes indicating a need to change something, it's your call as to how far you want to go with some of these items such as the OX sensors.
In some cases, the EGR ports might even be looked at for carbon plugging but is one of those items that comes under the heading of 'wait' for a fault code it might cause.
I limit my work to plugs and fuel filter, air filter over the longer term, with oil/filter being done every 5k miles.
If the truck for example has like 90k and never had plugs, fuel filter etc, it's more than time.

 

I change my plugs and trans fluid & filter every 100,000 miles. Oil & filter every 5,000. Grease the front end every oil change. Check the brakes every time I rotate the tires, (15,000ish) and replace them when they wear out. I replace my air filter when it gets about 1/4 inch thick in caked dirt. I ONLY use motorcraft air filters. They are coated with an oil film, and work MUCH better than any other brand. PERIOD. I changed my shocks at 215,000, and the old ones weren't even worn out. Waste of money. I replaced the O2 sensors at 150,000ish. Waste of money. They lasted that long, I should have kept on going with them. Fuel filters? Well, I have over 100,000 on the same fuel filter, and that's AFTER switching to a blend of E-85. I'm not planning on changing it anytime soon.

Soo..Tune up? Nah. Maintenence? Yeah. Use good judgement based on your truck's operating conditions. My truck is a farm truck, with a lot of idling, and VERY dusty conditions. I go through air filters like crazy. My mother's EXPY never gets an air filter. It never stopps up cause she isn't in the dirt a lot.