I just got a 11 silverado 1500 and am looking to put an exhaust on it. I went to the local muffler shop and they said they could give me dual single in/out flow 40's. I'm assuming that they are going to put both mufflers on my original cat converter. Is this normal and if the shop does plan on putting both muffler's on one cat should I go ahead with it? Or should I go with one flow single in/dual out?