Ford diesel trucks had lots of problems up through the 2010 model year. After that they have been considerably better and on par with GM and Ram trucks.
Diesel engines are best when not used for short trips where they do not get a chance to warm up properly. A 3 year old truck with 80,000 miles was not subjected to the abuse of lots of short trips.
I would want to review ALL the maintenance records for the truck. Very important that oil filter changes were done at 7500 or shorter intervals and that the fuel filter was changed every 10,000 miles or less. Otherwise you have a truck with an engine that is going to need work sooner and injector repairs in particular will cost more than a complete rebuild of a gas engine.
