I just got back from thangsgiving trip and hand calculated 14 mpg on the highway. Mostly running 75 to 80. I have a 08 6.4 with 5 inch exhaust afe air filyer and kem 345 tune. I also have a 6 inch lift with 35 12.50 20 tires. This seems a little low but is what i came up with. Anyone have any ideas.