Well the lift isn't what makes your mileage bad, it's the tires. When I lifted my car and had stock tires I noticed zero change in gas mileage. Then when I went to my 275s, which are muds,
I lost around 2mpgs. I did get some of it back with performance mods though. I get around 15mpgs now. I'd say don't worry about gas mileage. I was worried before and now I wish I had gone with a 275/70/18 or 285/70/18. The next set of tires will be bigger than the ones I have on here for sure. My mileage may suck,
but when I wake up every morning and look at my car I always smile and forget about it