Usually, a reduction in tail pipe diameter will pick up bottom end torque on the street, so that's a good thing. The factories knew it. That's the main reason it was done. Use an off the shelf kit if you want, but if we don't start supporting local guys trying to make a living, sooner or later, they'll be a thing of the past. I say check around and find a good local muffler shop. That way, should you have any warranty issues, you won't have to worry about shipping, inspection and all the associated hooah and you might even make some new friends.