Is everyone sure they are filling their tanks exactly the same? Fuel is very susceptable to heat, is your gas in the tank the exact same temperature as you initially filled? If the gas in your tank is colder than the last time you filled it will take up less space allowing you to fill the take more, resulting is a lower looking mpg. Mine is always really close. I also suppose there is a % that Ford might be off reguarding quality control with fuel metering.