I bought a 2005 K3500 4WD a few months ago. The first few months it wasn't worth checking the mileage since we had cold weather and I had some mornings where I let it idle so I didn't have to scrape as much frost. Checked my first tank about 4 weeks ago and got 18.21 hand calculated. Not to shabby, I thought. Last weekend I downloaded the 90HP PPE tune. Pulled down a 22.35 tank. Should have done it sooner. Only bad thing is keeping from testing out the extra HP.