This is the best mileage I have gotten so far in my 01 1500 4x4 5.9. The truck was only getting in the 9 MPG range when I got it during the winter. A complete tune up, bed cover and easy driving got it in the high 11's to 12 MPG. I wonder if the summer formulation for fuel has had a difference in mileage? It seems the mileage went up this month for no reason.
The trucks readout says 13.4 MPG but I calculated 13.0 on the last fillup.
I'm not sure how, but I average around 14.0 mpg all the time. I have a 70 mile a day round trip to work, and don't put the "pedal to the metal" too often. When I tow my 6x12 trailer with the John Deere lawn mower on the back, it does drop a little, but not much. I guess I'm one of the lucky ones! My truck is bone stock, with 140,000 miles on the clock, running 10w30 oil (not synthetic), and use 87 octane.