Ask yourself, why does a 5 year old truck need a new motor? its one thing if it was yours and you know why, its another to buy something you have no idea why it needs what it needs! especially a newer diesel. the 6.7 had fuel system issues that could`ve prompted the replacement so it may need more than just the motor! Out of all the new diesels I would pass on any 6.? Powerstroke! And despite my screen name I`m a diehard Ford guy.
Keep looking!
Edit: I didn't see your last post till after I posted. I used to work at a dealer and I heard stories like that before, that smells of made up salesman BS. I would still pass!