I have a 07 2500 with the 5. 9 in it. This weekend I took a trip to Fargo, ND. This was about a 340 mile trip. On the way up there I had about a 30 mph head wind. Driving 70 with interstate all the way. When I got up there I filled the truck and got 16. 5 mpg bucking the wind. When I drove home...