first time on here, I just got a 2005 GMC Duramax SierraCrewcab with a short box and am really pleased with it. Need to learn all about these things. I will be using the truck to go to work, 20 mile round trip, pull a 24 camp trailer, horse trailer and haul hay. Want to learn how and what to do to get best fuel mileage. This truck has 220k miles but looks and runs like new.