Last night, I was parking when I noticed my temp gauge was up in the red. It struck me as odd, because I'd been driving this truck for over a year with absolutely no heat problems.
I get out and pop my hood. All the hoses look healthy, the rad cap is in place, though the dust around it looks like it may have vented. Oh yeah, and my coolant resevoir is boiling over and running across the parking lot. I give her time to cool and spend north of four hours limping her the 20 minute drive back to the house, not being able to move more than a couple miles between cooldowns.
Even with getting up to 70, I had a slow, steady climb on my temp gauge. The heater being cranked up did seem to help me limp further, but it didn't seem to be blowing hot air. The fan turns, though I don't know how to tell if it's moving at the right speeds, but my gut is telling me that the water isn't cycling through the engine. I already walked to the parts house and bought a water pump, and thermostat, but before I tried installing them myself, I wanted to see if you guys thought it might be something else other than one of those two things.

 

those would be my first two guesses, thermostat being the most likely culprit. Since you have them I'd start with the thermostat, put it in fill it up with coolant and see what happens.
You could always just use water and drain it after if it cures your problem.

Most often when the water pump fails you'll see coolant leaking out of a "weep" hole behind the pulley on top of the housing where the shaft goes into the pump AND/OR you'll notice a squeaking sound while it's turning

If replacing both the pump and thermostat doesn't solve your issue, maybe there's a blockage in the system? With the engine COLD take the cap off the radiator and start the engine, you should be able to see coolant flowing.

You said you had no heat while it was over heating, there is one other thing that could be wrong (worst case scenario), a bad head gasket/ cracked head. My '03 5.4L had a bad gasket and it was pushing exhaust gas into my cooling system, overpressurizing it and blowing coolant out the over flow bottle and my heat would go away.

 

No heat when overheating is almost always a thermostat stuck closed along with an airlock.

 

Just for S&G pull the dipstick and make sure the oil doesn't look like a milkshake.

 

Good point