I recently removed the muffler from my 04. 5 and welded a straight/"cheater" pipe in its place. The sound is awesome,I've had it at varied rpms and no drone. I left the cat in place so there is no warranty/emissions issue {could be why there is no drone} Sounds like a big rig!!!!! Much more the cost is less than half of a cat back or aftermarket system. If you have the work done for you the cost should be around $120. 00 or so. In my opinion its a no brainer, less out of pocket money and still an awesome sound!!!
P. S. also have the turbo silencer removed and the air baffles
P. S. also have the turbo silencer removed and the air baffles