The big thing to always look for is the blown intake plenum gasket. Causes pinging, oil usage and poor mileage. The best way to check it is to shut the engine off and hold the throttle body wide open and look down into it with a flashlight. If you see a little puddle of oil the gasket is blown. We offer a repair kit (#7714) for it if you end up needing one. Other than getting about 13 mpg they are pretty decent trucks.
Good Luck & Merry Christmas!
Kevin @ Hughes