Okay so I'm guessing I need to match the CAT size to my exhaust. Right?
Well my truck had true dual flowmasters on it when I bought it and I'm not sure how to tell what size they are.Is there a way I can measure them? Any help would be much appreciated.

 

Do you need new cats or something? You should just go buy some magnaflow universal cats, they fit fine man!

 

This is my first truck and now that I've got a consistent paying job, I've kind of went into the Mod mode. I'm extremely new when it comes to mechanical stuff, so please excuse any stupid questions.
When I got the truck I was told that it has True Dual flowmasters but I have no idea of what size piping or anything. Well it is almost at its 177k mark and from what I understand about CATs is that they can clog up over time and reduce power and I guess effect exhaust sound. Is there something that I would defiantly notice if my CATs were clogged or effecting performance? With True duals isn't the CATS connected directly to the exhaust manifold? but then aren't there 2 cats in the back as well?
Wouldn't high flow cats also help my truck sound better? I mean my truck sounds good (Dad loves the sound) but I'm wanting to add a little more aggression to it. I'm thinking about Flowmaster Super 10s and the High flow Cats (if they help)
Any input would be nice, I'm always willing to listen and learn.
Also the truck is a 5.4l