The leak detection pump is mounted to the bottom side of the battery tray. It is kind of a pain to get the tray out, but it is not too hard of a job. It has emissions hoses too, so it would be worth a look to see if they are cracked. The smallest slightest crack in a hose is still enough to set the P044xx code.
The gas vapor canister usually only goes bad if you are prone to add more gas in the tank after the handle clicks off when filling up. I think it is best to start with the simplest and cheapest solution first, try a new gas cap, clear the code, drive the truck a few days and see if the code comes back. Gas caps do go bad fairly often, there is a seal in the cap that fails with age and it does not take much of a fuel vapor leak to set the code.
The P044xx codes are hard to figure out because they have a lot of different causes. If the code comes back after you get a new gas cap it might be worth having a shop do a smoke test on the truck. That would be the better way to pinpoint the problem.
Last edited by 01SilverCC; 12-25-2012 at 01:47 PM.