You ought to be fine with your standard 3.31 gears with those tires, especially if you have an EcoBoost F150. While new gears probably would help make your truck feel more spritely with those tires, the fact that you would also need rear gears and likely install kits for both, make cost/benefit of jumping up to 3.73s kind of questionable. Your better bet would be to get a custom tune or just adjust your current tune for the larger tires.