I don't hot-rod my truck, but it does get surprisingly good mileage. In town I get around 16 to upper 17. On the highway it gets around 20 mpg easily. On a recent long freeway trip I got 21.0 at 70 mph and 19.8 at 80 mph with the cruise set. Surprisingly, with all the monitors these trucks have their on-board computed mileage is extremely close to hand calculating.
Towing my 11K lb. trailer on a recent trip of about 4500 miles, I was getting upper 13s at 58 mph and 12 to 13 keeping it around 65 mph max. In the Canadian Rockies I was getting 11 to 12.5 towing. I also have the 3.31 gears which improves mileage.