Well I don't know how you guys get such great mileage but I have an 07 3500 6.7 DRW with 4:10's and the best I have ever seen in 7000 miles is 14 driving. Throw on the 14k trailer and that is HISTORY! Lucky to get between 8-10 on flat ground!
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'07 Bighorn 3500, 6.7 cummins/6spd auto, 410 rear Quad cab LB. 4x4 51 gallon toolbox/fueltank combo.