I have the exact truck you describe, 4x4 Pearl white exterior and black leather, sunroof, 12" NAV. I love it, the Hemi is an outstanding motor. I get ~12mpg in town with 37s. 16 on the highway. Stock i got 19 highway and 11.5 towing 8k pounds. Just installed the Pedal Commander and i love it even more.
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Again, just point out. You SURE ain't gonna get that kind of mileage in these parts with your rig. Empty, or hauling. Around here, the only way a 6.4 is going to get 11.5mpg pulling 8k lbs, would be off a cliff.