I had a brand new 2021 Classic, 3.92 gears and 5.7L and I installed a Flowmaster super 44 and had painful drone inside the truck, was super loud outside. Installed a ultra-quiet resonator before the muffler and only slightly more quiet, still had drone. So I took that out and out in a Flowmaster 50HD and was much better in the over all volume outside and drone inside, but with the 3.02 gears I still get that drone on the highway in 8th gear at around 1900-2000 rpm (doing about 103-110km/hr).
I’m considering putting the stock muffler back in, and also installing a remote controlled bypass valve That goes from stock to either open pipe or into the 50HD if it’s possible to fit space wise. That way I can go from stock to nasty and back at any time. And avoid drone on the highway with the family.
These trucks just don’t seem to be able to do any kind of aftermarket muffler change without some drone as a result. With the 3.92 hearing it makes it impossible to avoid drone, mostly at highway cruising speed (with the flow of traffic, not speeding at 120km/hr or more or limiting it to 7th gear and running at about 2300rpm or more).