I have a 01 F350 7.3 stock 4x4 crew cab long bed with a hard shell cover on it. Never have i got over 11 MPG with it ever and that was with a tail wind. I started to see a bit better MPG and found out that part of the seam blow off the muffler. so i put on a 4" exhaust on it from turbo back, then a 4 Banks chip and a very large air filter on it. 4 times larger air filter then was on it. Went on a trip with my dog and 1500# of rock in the bed of truck. On the turnpike and highway i was driving 70-75 MPH all the way. About a 350 mile round trip, i got 21 MPG with the wind and 19+ in to the wind. My 4 Bank chip has 50,75, 100 and 140+ on it, i was running on the 50 HP. Just before i got back i put on 75HP and my mileage started to get higher. I love my truck now and the power that i have is just WOW.