Me and about 5 million other members have been very happy with the MBRP replacement muffler from DPPI. It fits in the exact location as the stock muffler with little to no cutting required (some, myself included have need to cut about 2 inches off, some have been able to bolt it right up). It sounds real nice and deep without all the noise and interior resonance or droaning. Another option is to get ahold of Rip Rook @
http://www.protintnw.com/sa_dodgemenu.htm he can set you up with exactly what you are looking for. I went with the replacement muffler because you already have 4" exhaust made of 409 Stainless steel so why buy more tubing when all your restriction comes from cat and muffler? You can also buy a cat delete pipe from DPPI as well. Good luck with whatever you decide.