First of all, check with your local laws about changing the cat setup. It's illegal in some place to do anything but change your cat out for the same setup (single cat.) I've been warned many times (by inspectors and by a referee) about mine but since the truck changed before I moved to an area with inspections, they overlook it with a warning. Flowmasters are better for performance but not for sound. Borla, Magnaflow, and the like all sound better. Having cats to act as resonators helps tone down the droning sound from the Flowmasters. Without cats, it's very annoying and gets old for a daily driver. My 40 series Flowmasters are 12 years old and still going. The cats are Catco but I've replaced both of them in the 10 years or so they've been on it. One because of an ignition problem dumping raw gas into the exhuast then detonating one the cats. The other started rattling after about five years (before the detonation incident.) After I took it off I saw that the catalyst had separated from the housing and was able to shift around inside.