Just my .02, 2014 Seirra 5.3, magnaflow 12589, flapper moved to in front of the muffler, resonator removed, sounds really good. Very quiet at highway speeds, plenty of growl when accelerating. Only thing i dont like is when accelerating around town it gets a little loud in the cab with the windows up around 2000 rpm, windows down its fine. I ran it for a week with the resonator and flapper in original place, barely any noticeable difference from stock muffler. With flapper behind muffler there is a whooshing sound from exhaust, by moving it in front of muffler that goes away.
