Single exhaust cat back system. They sound nice without being loud. They seem to get a bit quieter around 3000 RPM, but at startup and revs up, and ESPECIALLY on the revs down, it sounds good. I have a friend who has a Yukon with 50s on it, and mine sounds better than his.
i got the flowmaster kit, i dont know witch muffler its got, but its not loud but its not quiet. i llike the way it sounds after 1500 miles, its gotten louder since day one. the install on the kit took about 3 1/2 hours, most of the time was removing the old system.......you can tell the difference in throttle performance, it makes me wanna slam the gas all the time. this summer i might be upgrading to a 50 or 40 series.
i have a flowmatser 70 on D and it sounds great at start up and when you get on while cruising you can barly hear it if you have the a/c on you cant here it inside at all and i felt a big pick up over my stock muffler i would go with a complete cat back system tho the factory pipe is just fine flow wise