I removed my muffler and put 2 magna flows up front and also removed resonators, with NO replacements. I will agree 1000%, it sounds sooo good when I'm on it, it's hard to not get on it. I will say this too, that once at speed, inside sounds like stock, quiet.My guess with the mileage drop, is that after you begin to hear how beautiful the Hemi sounds when accelerating at moderate throttle input. This leads to more rapid acceleration just to hear the motor, which leads to a drop in mileage when you hear almost nothing. lol just a theory, but so true for me!