I am going to jump in here and agree with Cody. Everything he has stated I have experienced on my 2003 F350 with a 7.3L in.
I will also say I get my best millege with the 80HP daily driver and never use the fuel sipper. On the freeway in the flats I can get up to 20MPG if I keep it between 65-70. I do not have a dually but it has 33" tires and a leveling kit.
Joe
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 2003 4x4 F350 Super Duty Crew Cab Short Bed
4" Down pipe and exhaust, Wicked Wheel, Modified Exhaust Turbo Housing, Big Head Waste Gate Actuator, PML Transmission Pan, Factory Tech Valve Body, Autometer Gage Pod, PHP FU2 Chip
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