I think everyone (v6 or v8 owners) need to keep in mind the testing that is done to determine the EPA numbers. For example, highway numbers (max speed 60mph, max acceleration 3.2mph/sec, avg speed over 10.3mile trip 48.3mph). I'm sure none of us drive like that. At least we won't until gas creeps back up to $4-$5/gal again.
http://www.fueleconomy.gov/feg/fe_test_schedules.shtml
It also really depends on the driver's foot. In my wife's Expedition, when I drive from our house to downtown Houston on nearly every Saturday morning, I average just over 19mpg but when my wife drives this same route in about the same amount of time it takes me, she averages just under 16mpg. I'm so used to driving in traffic everyday that I don't accelerate/decelerate as quickly as she does and I also tend to coast more rather than constantly pushing the gas pedal.
You mileage may get better as the miles roll by but you might need to adjust your driving style a bit to make more of an improvement.