What is this part?
 

I'm just sitting here at work and remembered a question I wanted to ask a while ago but forgot to. What is the black cylinder type thing that is mounted right in front of the spare tire? I can only recall ever seeing it on Fords (at least in that location). If memory serves me correctly, it has some sort of plug or sensor going into it, but that is it. Just curious.

I wonder if you mean the vibration dampner? It is on the drivers side rear of the truck right behinde the rear mount of the leaf spring.

No, I believe it's mounted right in the center, in front of the spare tire. It may even be on top of the spare.

Sounds like you're describing the evaporative emissions charcoal canister. It stores fuel vapors to be drawn into the intake for burning. It should have a white valve on it, that's the fresh air canister vent valve.

I went and looked and didn't see any white valve, but then again everything attached to my truck is completely brown at the moment lol. I would take a picture but I haven't seen my camera since my sister took it on a school trip about a month ago. You're probably right though, Quintin.

That's what it is.