Using your on board computer to calculate MPG won't be very accurate.. The only way to really figure it out is with a good ole pen and paper and a calculator

20+ with 37's?! Wow, that's impressive...

 

I drive in Eco at all times except coming off a red light getting up to 30+ I'm in Biloxi ms. Flat as hell. There is no way in hell to get 17mpg especially on the interstate. I drive 60-65 and stay in Eco at all times. Best I've seen is 15.6

 

16.8 and 17.2 last two tanks 6 speed with 3.21 I think it just varries by a number of variables

 

That's strange. I drive in Eco all the time as well and I get almost 20 on the highway with 34's. Is everything calibrated?

 

I've got gear and tire calibrated. It's on par with two different gps apps and all the radar signs around the town.

 

I do have a cyl 6 misfire from time to time. That could make a good loss I'm sure. Haven't been able to catch it in action when I bring it to the dealer in the last 10k miles

 

Thanks for the advice guys. Looks like I'll be regearing and getting a procal. Hell, maybe even a CAI and exhaust to get a little extra...

 

Pen and calc is the only way to check fill up the tank and reset the miles to zero check till u get the refuel light once it's lifted with big tires that mpg calc is out the window

 

Not sure I understand the pro cal recommendation. Sure it will correct the tire size in the computer, but if wont help with any lost performance?

 

The pro cal will only correct erroneous readings by using accurate diameter measurements. The increased rolling resistance of larger diameter tires AND the reduction in aerodynamic efficiency when creating additional airflow underneath the chassis contribute to poor economy. A change in gear ratios will help with restoring some power loss but shouldn't have much of an impact on improving mpg.
Honestly, the only suggestion I've seen in this thread that would represent a gain for mpg, is the increased tire pressure; The downside being very poor ride quality.
My '08 2 dr(manual) on 37's and 5:13 gears ran an average of 11.8mpg mixed use.
My '12 4 dr(auto) on 37's and 4:10 gears runs an average of 13.5mpg mixed use.

The biggest drawback to the design of the JK is the nearly vertical front windshield. In paying tribute to the jeep legacy of a fold down windshield, engineers are faced with an impossible task regarding aerodynamics. This is why you wont see a stock jeep on 35"s or larger. So, the best future hope for gas friendly wranglers is going to be raking the front glass back; With that single change, it's not unreasonable to see 18+ mpg on a lifted rig.