I guess I missed the GMC, my newer truck get's 12 mpg lol. In my experience, every truck I've ever owned got somewhere in the teens. So if you run the math, the difference between my pickup at 12 MPG, and my FJ Cruiser at 17 mpg, at my current local price of 2.45 a gallon, driving the FJ daily would save me 901 dollars per year. La Di Da...
If you're driving a truck, they all suck for mileage, period, may as well drive the one you like, because the cost of driving one you don't like, isn't going to save you a thing. I'd have to go up over 25 mpg for it to make enough difference to matter, and I drive a legit 15,000 miles per year.