ORIGINAL: scarpones
Actually now that I think about it...it sat with about half a tank for a week or so. You think that would of been the problem?
It's a good possibility. It's good practice to run all the fuel out of your truck at the end of the day. The fuel can spoil quickly, and also leave oil residue in your tank, lines and engine.
At the end of the day, empty the tank, then fire up the truck till it runs out of fuel. This should keep things nice and clean.