Once again I would suggest that you get into the codes to see if it is one cylinder misfiring or all of them.
You can has an oxygen sensor built into it to tell the computer if it is running rich or lean. Some scan tools allow you to read the data out of (among other things) the oxygen sensor. If the car just seems to be running rich and the computer has backed down the adjustments all the way (you should also be able to read this with the tool) then perhaps you have a leaking fuel injector.
If you intend to try and fix this yourself, I would suggest that you consider investing in a tool like:
http://www.obd-2.com/ (I have no relationship with them other than being a happy customer).
If SC has an emissions testing program then you certainly will have a problem if you cut off your CAT as you will fail the certification testing. It may make the car sound more aggressive but it will also change the shape of your torque and horsepower curves. The 3.5 (IMHO) doesn't have enough low end grunt as it is and cutting out the CAT will only make that worse.