It can be many things...wind terrain etc..best thing to do is try to find the sweet spot and run the truck at that speed among other things.
There is an awesome app. To see the current wind speed and direction. I use it all day long to adjust and save fuel along my whole trip.
Brand new truck....less than 23k miles in 3 months and the it had a bad oil leak the other day. Turned out the gasket was already bad and replaced. Done under warrenty, but ####.......
Sounds about right. When I got my '17 it was down in the Dealership for a week for driveline issues before 15K miles, then immediately again afterwards for OneBox issues.