[LS short box]

No muffler expert by a long shot. I'm running headers, 3" collectors reduced down to 2.5", then non-xpiped to the bumper. Running Dyno Max super turbo mufflers. Zero drone.
But when I did the cab insulation I put down a layer of dynamat like insulation then the double foil sided jute insulation. Then the carpet. Did the insulation from the firewall to the back of the cab to where the gas tank would of been. Again zero drone.
One more thing. When I was much younger I worked for a Chev dealership and we were the first with a exhaust pipe bender and the training we had from the supplier was that the first exhaust hanger after the manifold was at the muffler. It gives some flex to the exhaust system.