Genxer

With the right body shape, a car only needs a few HP to cruise at hwy speed. Speed changes and the occasional naughtiness probably account for most of the difference.

JIM5.0

The Coyote is very surprisingly a fuel miser, often getting above the advertised 26MPG on the freeway at 70MPH.
I attribute that to the very high 11:1 CR and the TiVCT which goes into a fuel saving cam timing during cruising.
Even in bumper to bumper rush hour traffic with speeds crawling as low as 20MPH and many dead stops and go's, at the end of the week, my AVG MPG is still above 20MPG. My AVG MPG read is 20.7MPG right now as we speak.
On the freeway, I have driven 100mi on a relatively flat freeway at a steady 70MPH and regularly hit 28MPG AVG and with good a tailwind, as much as 30MPG.

If I hit the reset and begin clocking my AVG MPG only for the parts that I am cruising at 70MPH, I see it reading over 30MPG AVG for the 70MPH leg of the trip; these legs lasting as long as over 70 miles and my AVG MPG never drops below 30MPG.

UPRSharad

My 2011 5.0 M6 averaged ~22mpg NA in the city and it averages over 24mpg with the ProCharger! It's pretty economical for a 10-second car!

J7erry

GTC, I just did the same thing! Traded my 2013 V-6 Premium for a 2014 GT. I averaged 24-26 to work in the V-6. While I have almost 500 miles on my GT, my 2 half tank fill-ups, I averaged 22.6 and 23.3. That is calculated mileage, not gauge. Haven't taken a trip yet in the GT, but I averaged 30-33 hwy with the 6. I'm sure if I drove it like I stole it the mileage would be lower, but gas is too high. I'm sure after my break-in I'll have fun with it though.

GTC

4,700 miles on GT now, 21.2 mpg overall. 23mpg recently on 200 mile trip at average 85 mph and 97 degree ambient temperature (even with additional Ford oil cooler the oil ran just a wee bit warmer than usual but needle still centered on gauge nowhere near yellow); 25.4 mpg on return leg at 72mph and 8 degrees cooler ambient temperature.

Get about 1.7 mpg less overall than V6, and 4mpg less on highway, but drive the GT a little quicker, and I tend to make myself grin on on-ramps by punching it in 3rd gear.

Interestingly, with cruise control on going up fairly steep interstate grades the GT never downshifts out of 6th gear (Auto Transmission obviously). The same stretch of interstate would have the V6 dropping from 6th to 4th gear four or five times. So the GT is leaving highway mileage on the table by not having a taller additional 7th gear to shed some rpm and take advantage of the Coyote's power.

Can't really see the 2015 GT having a big mpg jump since they stayed with six gears unless they've reduced friction dramatically and are doing cylinder management (just firing needed cylinders depending on demand). Ford is saying the new GT burns fuel more efficiently. Would love to see another 4mpg overall. And, Would love to see an 8 speed auto with a dual clutch (e.g. new Acura TLX V6 has a 9 speed auto) and Ford and GM are jointly developing some of those boxes for the future.