If one of the cats if plugged it would cause a loss in power. You would have to step further on the gas to make up for the power loss and it may cause some noise in the intake like its having to suck harder due to the back pressure. You can connect a vacuum gauge to the intake to check. Its not 100% but should give you a good indication. If the vacuum drops way down when you open the throttle to a fixed position and stays low and or bounces real bad I would look further.