Just did a 312 mile round trip (almost all highway) up the PA turnpike to Pittsburgh from northern MD. I averaged around 15.8 MPG @ 72 MPH. I have 33's with 3.73's, and the speedo corrected with Procal.

 

pretty much stock jku hardtop 3.73 and I am getting 15.4 around the city. I don't know how the 3.8 was but gas mileage isn't something I would brag about.

 

2012 stock /auto /2dr/4.10/rubicon. flat/ low hills terrain, 850ft elevation avg. 15 city /18 mpg hwy (70 mph)

 

So overall it's not looking that different.........except for the fact that you're getting better performance wherever you go.....which is a good thing.

 

I went from a 2008 JKU with 35s, 6 speed and 4.88 gearing getting an average of 13.5 mpg to my 2012 JKUR with 34s, auto and 4.10 gears and now get an average of 14.5. All my driving is city stop and go. The added power was worth the change but I was hoping for more than a 1 mpg improvement.

 

They are only rated one mpg higher on the window stickers from 12 to previous, wouldnt expect much more than one better considering same options

 

2012 JKUR 6-speed, 1900 miles on the odo.

Best tank was 18.8 mpg
Worst tank was 13.3 mpg
Avg is 15.5.

 

15/18 here mixed driving

 

12JKUSport just hit 300 miles and I get 13.5 combined only mod is teraflex leveling kit

 

Yup. Easier to give a box more HP than MPGs. If you can't move it more efficiently, move it faster.