Originally Posted by RamTech
I agree with much of this. Even with the A/C on while moving at highway speeds, it's unlikely the electric fan will come on. Messing with the cat is a bad idea, IMO. One - because I've never seen any imperical evidence that there's any mileage to be gained and two - it will kill your warranty.
Would it just be smarter to replace the headers and the rest of the exhaust?
If i did mess with a Cat, i'd probably go with a dealer approved high-flow cat.