are you down to 11 miles per gallon too? since i put 35x12.5 20s on mine the gas mileage has plummeted.
Hey Joe, are you getting your mileage calc from your computer? Because the computer only knows how far the truck is moving by calculating wheel revolutions.
Increased diameter means the truck is actually travelling farther than the computer thinks. You added 2" to your tire diameter, which means the truck is moving 6" further every time it turns. The difference moving from 33" to 35" tires is 6.1%. That would be enough to drop your comp's calculations a bit.
Plus you have increased rolling friction from larger tires. And if you're not running high enough tire pressure, that's adding to it, too.