Check my signature. I have gotten AWESOME fuel mileage in my truck once!!! But I regularly see 19+ to 22mpg on long freeway trips. For the best mileage I leave the chip set on the 100hp setting. Inflate the tires about 5-7 psi over optimum, but never over what the sidewall says. I do not use the cruise control in the hills, I only use it on flat ground. I try to keep the rpm under 2100 and the EGT under 675-725. My typical cruise speed is between 68-72mph. Towing a 10k trailer the best I have gotten is right at 17mpg.Hope this helps.
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Late 99 SD PS CC SB 4x4 Lariat. 7.3l TS 6xchip Stock-140hp , Banks 6gun, Full Banks Gauges, 4"SS turbo back exhaust, UMP Intake w/ Donaldson Filter, Auburn posi F&R 3.73, ATS Trans W/ 5Star converter and CoPilot, 18k trans cooler, Dynatrac FreeSpin front hub kit, ITP oil X over, ITP boost regulator, Aero Fuel Tanks Replacement 55 Gallon tank, New timing cover,oil pan,oil cooler, water pump,turbo petastel, reman HPOP, new fuel filter housing, slotted brakes all 4 corners W/ Ceramic pads, Adjustable trac-bar, Front 1.5" level kit only. 226,000 miles 10/1/09 Best mpg 27.3..Norm city 15 mpg hwy 20+