Based on the OBDII sensors:
The cats are running plenty hot, all four of them are above 900 degrees, and higher when driving. They seem to be working quite well from that perspective.
The specific test that fails is this one:
Does this voltage being low represent a lean or rich condition?
The fuel trim seems to be within the +/- 15% all the time. They Long term trim levels do get upwards of 14.1% when driving at freeway speeds up an incline.
I'm wondering at this point if the fuel pump could be struggling and causing a lean condition pushing that one test below the threshold?
I've also noticed that while the light tends to come on after a fill-up, the specific test in question starts failing when the tank is almost empty; another peace of evidence pointing towards a lean condition.