How restrictive is the oem muffler, and why? I would think that, in the interest of better fuel economy and such, that a good flowing exhaust system would be attractive to the manufacturer.
Also, is there a muffler out there that fits without any modifications? I have the dual rear exhaust. It has a nice rumble at idle, and the sound inside the cab is not too annoying. I understand that there is more than one dual rear exhaust system from the factory, the one for the Sport models being more "aggressive" sounding. Never hearing one of those, I can't compare.