Mpg after lift?

First I know this is a truck so its not going to get 40mpg but with my 2012 dcsb v6 4 wheel drive I'm getting 21mpg mostly freeway driving. Over the weekend I got a set of wheels. Size is 265/70/18 they rub very little and was thinking about a 3" lift kit. Wanted to see what kind of mileage I'm going to get with the lift. Like I said I mostly freeway drive 80 miles a day. Or should I just level it out? Thanks guys loving this truck so far.

 

I have a 3" lift with 285/70/17's (32.8") on my '06 AT 4x4 and get right at 17.2mpg combined freeway/street. I drive about 40 miles a day freeway, and about another 12 on side streets. But, my truck is 6 years old and still has factory gearing.

 

Thats not bad!

 

I'm ok with it but wish it was better. Winter gas mix and not having to run A/C is helping, too. Let me also add that I have a K&N CAI and an AeroTurbine 2525 muffler.