Sorry i should have included more info......
I have a 87 octane performance, 87 octane MPG and a 91 octane boost tune. i do drive the same route everyday to work and just cruising ill average between 15 - 20 miles per tank less with the 91 octane boost tune. What really made me keep my eye on the fuel mileage is about a month ago i took the flex on a long trip and i installed the 87 octane MPG tune and something was definitely wrong by the time i got to half tank i only went 125 miles, freeway no traffic cruising 70 - 75. Stock i get 200 miles at half tank.