If you are not 100% committed to installing an aftermarket muffler, my reccomendation is to have an exhaust shop remove the stock muffler, resonator and the V4 flap, but have them clamp the after market muffler you choose to install. Exhaust piping is pretty straight forward and easy to replace.
I currently have a flowmaster super 10 series race muffler on my 2014 silverado, it is the loudest aftermarket muffler flowmaster makes. Ive noticed that the 2014 and newer silverados have a lot of sound denizening and i have no complaints on any drone noise. Personally i like to drive with the tow mode on because it lowers the gearing and is more responsive. On a cold monday morning when im on my way to work and hit the cold start bottom, walking out to my truck sounding like a freight train always puts a smile on my face and pisses off my neighbors reminding them its time to wake up.
I will be adding a sound clip soon.
I hope this was helpful.