I have a RC 5" lift with 35" toyo MT tires. I lost 2-3 MPG and now get between 9-11 depending on where/how I'm driving (I don't drive fast). When I pull my small loaded Toyhauler, I lose about another 3-4 MPG!. Mine is a 3/4 ton Crew 4x4 with a full bed and 3.73 gears, so it'll get about 1-2 MPG worse than most 4x4 1500s. My odo was set as high as it could be by the dealer (33" tires, since thats what comes on the Powerwagon). I manually calculated it once, and to my surprise, the onboard computer was almost exactly the same.