hello there l have a 2006 hd sierra, what you truck guys are missing is that when your catalytic converters plugup your exhaust is not working very well,l'm thinking of magnaflow catback system,l know there is some cutting of the pipes but they don't offer what l'm after,so look's like l'll be cutting some of pipe no problem.l know the sound will come out great!don't be scared to change out your catalytic converters too.l had a 97 chevy sliverado and change the cats with new flow-master big differance.sold the truck milage was high sorry to let go but l'm happy with my new beast.when add cold with exhaust you will notice a big differance in power!there is no need for power chips or programers you can achive stock power with exhaust and cold-air intakes.