I had a 2005 Silverado 3500 that I bagged therefore the exhaust would work. I had them remove it from the catback. On my 2006 Yukon lowered 5"-6" I took the stock Duramax exhaust and they cut it at the Y pipe merge, welded in on and put in a Borla muffler. Right now with the stock manifolds and cats it sounds really good. Now once the larger cam motor, long tubes with 3" feeding that Flowmaster dual 3" to single 4" it might be loud. If so I will throw some resonators around where the cats were. Just check with local muffler shops to see if they remove stock 4" Duramax system. It works great and fab was minimal.

 

I had the 4" Corsa catback on my old SS. Fit great, near silent inside, but ear blistering outside. Got pulled over more than once because of how loud it was. Finally got rid of it when the internals of the muffler started to come apart. Couldnt stop the rattling inside.