Take it to an indy ("borrow" it) for a couple hours, have him pull the codes and do a thorough inspection. It could be something simple like a crankshaft sensor. The door handle issue is a snapped carrier, that's no big deal.

If there's nothing major, I would go back to the dealer and offer them $6,000 for the truck. They're going to have a hard time selling it at any price if the CEL is on and people can't even open the freaking door.