i agree, you won't get 5-10hp from a muffler swap..... Just like the dodge dealer saying the ram gets 28mpg........ Sure doing 70 downhill maybe. I have a flowmaster 50 series SUV muffler on my 4.7 ltr Grand Cherokee that my wife drives and it has a drone at 2000 rpm's and she hates it and wants me to put the factory muffler back on. We didn't notice and hp gains from that muffler swap. I like the sound of the muffler for sure, even at an idle it sounds deep and mean but i think that's the only benefit is the sound.
I'd rather be cummin then strokin