Code P0430?

I just bought a 2011 Tundra with less than 100K on it.
Check engine light came on, so I ran a code reader on it and found a P0430. The vehicle's Engine Control Module (ECM) has detected that the Three-way Catalyst Converter is not working properly.
The most common fix for P0430 is:
1. A new catalytic converter, followed by replacing the Oxygen sensor.
2. An oxygen sensor not reading properly
3. an exhaust leak
4. malfunctioning secondary air injection system.
So, how do I tell which it is?
Exhaust isn't leaking anywhere I can tell. I mean, it looks like its all in good shape.
If its the O2 sensors, looks like it could be any of the 4, is there an easy way to tell which one?
Any ideas would be appreciated