That really depends on what you're doing with your truck. An E-rated tire is perfectly fine if you're going to make use of the ply count and want some extra protection from brush, terrain, and debris. The engine and transmission can handle an E-rated tire just fine, though you will take a fuel economy hit, especially on the stock tune. That being said, if you're just doing the occasional jaunt on a forest road, than a P-rated/C-rated tire would probably be fine and hurt you less when it comes to fuel economy.