I finally checked the mileage on my stock 07 XL, standard cab, 8' bed, V6, auto, 22000 miles, stock wheels and tires. The past week, mixed driving...approx 70 percent highway, but about 100 miles of that with a very non aerodynamic 1000 lb load in my bed, I got 20.6 mpg on 87 octane regular. I normally travel between 65-75 mph on the highway. I was happy with the results.
