Here you go
http://www.fueleconomy.gov/feg/Find....n=sbs&id=38697
Also on the sticker
I was looking at the duramax. So 29mpg for the z71 and 22 for the zr2
On the zr2 it's not just the lack of valance, the bumper is mostly gone I front of the tire.
The standard bumper still blocked a lot of air. I'm thinking it allowing the air to get up in the top of the wheel well and it's acting like a parachute.