So i heard a rumor that all 4.7L's have the TRD performance catalytic converters...not sure if this is true...I do not have the TRD package so I was just wondering. I changed out the stock muffler with a Magnaflow series 40 muffler and new pipes, but didn't get chance to ask about the cats. Anyone know? It is also my understanding that changing out the muffler alone will not give me much, if any at all, improvement on performace (just sound) unless I was to upgrade the cats as well...true??