Usually 2.25-2.50 is the rule of thumb when it comes to exhaust pipes on a stock vehicle. 2.25 will do just fine on your setup, you will not tell a differece in going up an extra .25 in sound or performance if you went with the 2.50in pipe. (but your wallet will pay for the slightly bigger pipe lol) Im going with 2.25 on my truck as well. I have 2.00in pipe going to the muffler and 2.25 exiting the muffler to the tips. Im gonna put 2.25 in pipe in place of the 2.00in pipe that is going to the mufflers now.