Our truck came with 3.55 gears from the factory, and we didn't feel the need to regear for its 305/70R18 ATZ P3s after we tuned the truck for the tires. A truck with 3.31s will feel a bit sluggish with 35x12.50" tires, regardless of engine option. Still, getting a tune or a custom tune is usually a much better option than regearing, since doing the front gears, rear gears, and master install kits for both push you to the $1200 mark before install, while you could get a tuning device for half that price or less. That being said, regearing will definitely help make your truck feel more spritely, especially if you jump up to 4.10s or 4.56s over the 3.31s.