I purchased a 2014 Ram 3500 this summer. It had 35 12.50 18 BFG AT on it. I just replaced them with Toyo AT2 in the same size. The Toyo has a slightly more aggressive tread pattern than the BF that I just replaced. Today I pulled a Jeep down to Alpine. Fuel mileage was awful. The readout was 10.8 mpg. Prior to the tire change the truck would typically average 12.5-13 pulling similar weight. Tire weight between the two tires is equal(within a couple pounds). I have a hard time seeing that much of a performance drop just from a slightly more aggressive tread. Truck does seem to downshift more from 6th to 5th gear also.