I have a set of 275's on mine with the 5.3 and I am glad to see 13 mpg without a trailer. If i hook up a trailer go ahead and look for 11-12. I avg 12 on a good day with a 700 ATV in the back. All these ridiculous mpg numbers must come from people driving 45 with a tail wind, stock tires, and easy throttle. GM fuel economy sucks. I have a 2011 Ford F150 work truck with the 5.0 and 3.73 with factory 20's and that beast will out tow, out run, and out mpg this 5.3 any day. It gets an easy 17-18 with the ATV in the back. It may dip considerable with some decent tires though. If Fords werent so damn ugly I would get one. I like my Chevy, but when I need a good laugh I troll for people boasting fuel economy. And, the DIC is wrong more than it is right, it apparently was built by an optimist.