I've got a 2007 Suburban with the 5.3L V8. I'm getting 12.4 MPG in the city and around 15-17 MPG on the highway. Really sucks intown but what can you do. I've noticed you can buy "chips" on e-bay that will increase your horsepower and also increase your gas miliage. I've always wondered about them. I'm guessing they can't be too good for the engine. There's a reason the fuel settings are set the way they are. I'm afraid if I mess with it something else will break down. I don't complain too much about my gas miliage. I knew going into the purchase I'd be paying more a month for gas. Something you have to live with I guess.