I saw this post and was surprised not to see a 2.25" recommendation. When I originally got my TRD header and cat-back, the TRD tech/engineer I spoke with said the 2.5" option was for non-header applications or for when they also installed the supercharger. I explained that I pulled a 3500# boat and didn't want to lose ANY low-end torque. He insisted that I get the 2.25" cat-back in combination with their header to keep the torque curve similar to stock. The most obvious benefit after the upgrade was that a previous flat-spot in second gear on my automatic-equipped truck seem to be replaced by much better acceleration. <img src="/forums/images/graemlins/kewl.gif" alt="" /> Brew