In my 2003 Silverado with a 6" lift and 35s, and ARB bumper and about 200 pounds of "stuff" I went from 18 mpg to 13 mpg when I lifted it at about 35K. I drive it pretty hard and I just did an overhaul at 180K. New front suspension and transmission. Each side has had a new front hub and I am only on my 2nd set of brakes. Other that the gas mileage hit, I do enjoy what it gives me. It is not a Crawler by any stretch, but it gets me through mud and snow that stop most Jeeps when hunting, and that was my goal. For 4-Wheeling, IFS full sized trucks are not the best choice.
I run Bilsteins, which are lifetime warranty and were installed with the BDS lift. I have swapped out all 4 at least once, but it is like 20 minutes with air tools per shock, so not a big deal.