u/AppropriateCup825

Looking to add a Borla Atak muffler to my 2024 5.3 Trail Boss Lt. I am new to this and from looking online, I have found people either using part number 400958 and 400823. Also some people recommending to remove the flapper valve while others recommend to keep it on. The idea is to have the truck sound better, especially when getting into it but not be too obnoxious when driving in a neighborhood. Any insight is appreciated.