If you have 35” tires on your Ecoboost, you have essentially tallied your gear ratio. So, your RPM will sit lower while cruising on the freeway. To fight wind resistance and heavier tires, your engine will be significantly lugging at those low RPMs and using a lot of turbo boost just to maintain speed. This will significantly lower your MPG and add a lot of stress to your engine. To prevent this, you either re-gear your truck or lock out 9th and 10th gear so you are cruising at a higher RPM, preventing lugging and unnecessary turbo boost. Doing this well will also prevent high temperatures due to more coolant flow.
After doing this, I’ve noticed about a 2 MPG increase in my daily commute. I essentially lock out 9th and 10th on the freeway. During city driving, I lock out 8th, 9th, and 10th.
Try it and let me know if it helps you.