So I have heard it all about the 2008 6.4L mileage sucking terribly. My question is how bad is everyone getting with oversized tires? Truck is Brand new and I have put 4500 miles on it so it is no where near broken in and I realize this. I replaced the stock 265s with 38x14.50R20 and an 8" lift. Tires went on at 500 miles...avg over the first 2000 miles was 9.6 or so, and last 2000 has been about 10.4. Probably 60/40 highway/city mix. Is something wrong? I figures even with the tires and a non-broken in motor I would be at least 12.5 -13??