Make sure that's not just the tip.
My '03 GV with the 2.5L has 2" ID pipe all the way to the back of the truck and then right at the tip it steps up to something about 2.25". 
Just measured the pipe ahead of the muffler. Circumference is 7", which I think comes out pretty darn close to 2.25 diameter....so it might actually be 2" inner diameter. However, the outlet of the y pipe after the down tubes, which leads into the 3rd catalyst, measures just less than 2" inner diameter. There's some room for improvement there no matter what..
Your results may vary.