Gas Mileage Help!!

[bellyman14]

Hello everyone! I have a 2010 F150 4.6L with K&N Cold Air Intake, Flow Master 50 Series exhaust, and Edge CTS with the custom tunes for all of the above. But my gas mileage is still around 14.9 and 15.1. I once had a oil additive called Best Line before I had the above and I was in the 18.7 to 19 range. Could that additive have made that big of a difference? Are there better oil additives I should be using? I have always thought oil addivites are a waste of time.

Other facts, I have about 25,000 miles. I have always used full synthetic. I do not slam the gas everywhere I go and I try to watch the Edge to control my MPG.

Any help would be greatly appreciated. Thanks GPH Forum!