You won't lose much gas milage, I drive an '07 yukon with active fuel management and my average is 15mpg, and with that you have to take into account that I get 3mpg coming up lone pine, and about 8 coming up 138 to Hwy 2. I can see this information at the touch of a button and if I have it turned on, I tend to be alot more concious of my driving habits and may even slow down a bit to get better MPG.