Answer: Any check engine lights? If the check engine light is on and has a code p0420 it is possible that the cats. are plugged. One sure way to check is to check the temperature using a laser temperature gun at the beginning of each converter and at the end. It should be reading as much as the same. If the lower end of the cat is reading lower temperature possible clogging has occurred.
Other ways to check for plugged catalytic converters is to connect a vacuum gauge to a vacuum line and rev the engine at about 2500 rpm. A normal reading is anywhere between 16-21 psi of vacuum. Also you can take out the oxygen sensor on each bank before the converter, one at a time, and install a backpressure gauge. With the engine running and revved up to 2k RPM there should be no more than 2 PSI of backpressure.
There are other things that can cause the condition you have. The mass airflow sensor (MAF) could be faulty, low fuel pressure, multiple engine misfires, etc. The multiple misfire can also cause the converters to be plugged up if running this way for a long period of time because a misfire means that unburned fuel is entering the exhaust and igniting inside the converter, which will melt it. This will usually also have a flashing check engine light.