Iv been clearing 15-16 with a mix of in town and highway driving .I'm on the highway for 5 miles of my 7 mile commute to work, plus any in town errands I need to run. In all honesty, I consider myself to have all 3: towing, performance, and fuel mileage. This is the most powerful and fuel efficient vehicle Iv even owned.

If you want some better fuel mileage, you can follow the diesel guys: less restrictive exhaust from the turbos back, better intake, and tune it. They say theres a LOT of power and fuel mileage to be had with simply swapping out the downpipes with a better set.

Take this with a grain of salt (or aggravated assault, however you want): you've got turbos, so you don't need backpressure. Open up that exhaust and let it BREATH. As long as you can handle the raspy 6 cylinder exhaust note

 

The backpressure is caused by the turbos...typically for every pound of boost the impellor creates about 40% of the restriction.....the oem exhaust systems will easily flow everything that engine will put out as far as CFM goes.....basic math/physics.

 

I've read this thread because I bought a '13 FX4 EB last August. Very pleased with towing power, ride and comfort, etc, and with the mpg. It had 17k miles when I got it, and was purely stock. Still is. Now has 22.4k miles. Other than oil changes, I was getting 15.5-16 mpg using 91 oct. Around 21.5k miles I replaced air filter (with OEM) and added Lucas fuel system/injector cleaner. Boom! 17.4 mgp over 3 fillups.