My truck is a '12 SCREW...Great Truck!!
I'd take it to another shop and have an inspection done. Beyond that, get on a creeper and roll around under there looking at the undercarriage...is it torn up from contact with dirt and rocks? Is there any dents around the back of the cab/front of the bed? Around the edges of the bumpers?
Look at the shocks, are they the 2.5" ones or 3" ones? If they are the 3" you need to confirm that they are NOT the Gen2 shocks swapped onto that truck. It's a popular swap these days, and it's not a good idea at all. Search the threads on the forum here for info as to why...If the shocks are original, you are in for a rebuild (minimum) or a replacement, no getting around it. These shocks only go about 50K miles before service (rebuild) is mandatory. Again, search the forum for info, it's too detailed to explain in a quick response...
RESEARCH RESEARCH RESEARCH
It's on you do gain the knowledge of what to do with the truck. Most all service people and dealer mechanics and service writers are ignorant of the truck and what things are what.