Several people are greatly exaggerating the size of 35s, and the fuel economy difference between properly geared 33s and 35s.Fantastic explanation! I have considered making this point in response to many of the posts regarding tire size and mpg but opted out because I couldn't articulate my explanation this well.
My truck came from factory with the same 315/70r17 size tires and 4.10 gearing. I added 37s and 4.56 gearing and did zero lift. I gained 2 MPG over my stock factory original truck by going to steeper gears with the bigger tires. My effective gearing is steeper than factory setup with original gears/tires.
The easier the engine works the better your fuel economy will be.