Like most people, I am averaging 10.5 ~ 11.0 mpg tops. And that's mostly city driving and mostly light foot. If you are worry about gas mileage, this may not be the truck for you.
BUT do inform your wife that most full size "and" mid size SUVs out there are gas guzzlers as well. I think it's safe to say most of them get low teens in real world. So depending on how many miles you drive per month, the difference in gas money may not be as much as you think
