More like 7-9 mpg.... No really I get 9-12 with mine since it was new. 190,000 on it now. It has been reliable but I have also had a chevy with a 6.0 gas motor and that will out pull my 7.3 and get the same mileage doing it. My dad has the 8.1 chevy gasser and that thing is an animal! This will be my last deisel. More so for the following reason. !st, I've always got a trailer with toys that need fuel too. Very fuel fuel stations have pumps set up where you can fuel the tow rig with deisel, and toy toys at the same time. Minor I know. But it can be a real pain and time comsuming moving around, you deisel guys know what I'm talking about. Deisel now $1.10 a gallon higher than gas. The stink when idling in front of the house will warming up in the am. The stink when fueling and trying to get it off your hands and shoes. The ground is almost always caked with spilled deisel around the pumps. The 16qt oil changes at $5 a qurart oil. Oh yea, and will it start when we get back to the truck at -20???? Mines good to about -10 but anything after that, it's time for a block heater or forget it. It's all these combined that add up to a gasser next time around for me. I use the truck little as a car, so I don't care that you may get mid teens getting groceries with it. When used as a truck, you can do compareably well with a gasser without the headaches.
My .02