I have a beast truck. 2006 Silverado with 6.6 Duramax (LBZ)turbo diesel and Allison transmission. I get 13-14 mpg around town with lots of stoplights. On the highway at 55-60, I average around 19 mpg. On interstate at 70, average is 17.5-18.5. Empty this is 7700 lb., 1 ton extended cab, dual rear wheels. Haul or pull just about anything I need, including tree debris to the landfill, or 8000 lb. concession trailer and still get 11 mpg at 65-70 mph. 150k miles too. Many times thought about downsizing and quickly realized what I'd be giving up. Having no payments is also good, and no DEF needed.