This is my 2020 GMC AT4. I couldn't find exact details anywhere on how exactly to go about a muffler delete in detail. So here it is. I made this video for people who would like a muscle like rumble but not overly loud and obnoxious.
I simply removed the muffler and welded in a custom bent pipe. Everything else in the system remains the same. Both flaps are in and both resonators. The flaps keep any drone sound from happening while cruising. On cold starts it is loud enough to hear from inside the house or backyard but after 30 seconds or so it flattens out. It has great sound on take off and is quiet in the cab at Cruising speeds.
If you live in the Niagara or Haldimand area here in Ontario I got Heemskerks exhaust shop to do this job. They are located on HWY 3 in Wainfleet.
Thanks for watching