Why do I keep getting catalytic converter codes.

TRUE for a TSB, it may be online, its for a computer reflash, when you replaced your cats before, did you use new Toyota parts, very expensive or aftermarket parts. AM parts are not very reliable. You should not replace parts without proving why a code is thrown, a shop with a good scanner that can monitor data that appears to be like an oscilloscope trace would be fine. It is possible that the cats are weak now and the rear O2 sensors are active when they should not be active, meaning the cats are weak, not a problem with the O2 sensors.

You cannot have any air leaks, exhaust leaks may be a better name, this will skew the O2 sensors, even a pin hole so beware. If you have an IR temperature reader, the inlet to the cat should be 50 degrees F less than the outlet, if not after a drive and a quick check, then the cat is not good. With a scanner be sure the Readiness Monitor has completed also. Check for a TSB to replace the manifold on this model also. Ask the dealer about special service campaign 601. All cats must have a long warrantee such as 5 year, 50k miles, check your receipts.