Ok, so its probably a little late for this topic since I already purchased the TRD exhaust (Got it for $320 on eBay, BTW), regardless, here goes nothing. I measured the diameter on the TRD exhaust tubing and it is 2.5". I have looked around on the 'net and most of the catback systems are 2.5" as well. So my question is, why are they any better? I am assuming that since the tubing on the TRD portion of the exhaust is 2.5", that the cat to axle portion is 2.5" too?