Well as you know that HD trucks arent EPA rated, but with the 6.0L gas people average 8-12 in town and 10-15 on the highway. As to the diesel you can average 10-15mpg in town and 12-20 on the highway depending on the options etc etc. The big thing in a decision for diesel or gas is not only how much you tow but also availability of Fuel, here in northern MN there are alot of places that it is nearly impossible to find Diesel, and we also have the issues with the cold thanks to diesel gelling.
You will also have to buy urea for a 2011, and they have had some problems in the winter with the urea freezing.Our new trucks that we bought got crappy fuel mileage at first ( 400 km to a tank ) the best we did was 500 km to a tank.
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