Why would you think that when getting a larger displacement with more HP and Torque that you would get as good of mileage as a 5.9?
I would love to get better mileage also but when I need the power I gladly accept that power costs mileage. The 5.9 was not a perfect piece when it came out I am sure so if your not happy go to the 5.9 but when they get the 6.7 worked out you will be sad.
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'07 Bighorn 3500, 6.7 cummins/6spd auto, 410 rear Quad cab LB. 4x4 51 gallon toolbox/fueltank combo.