2013 GMC Sierra 1500 5.3L Engine P2271 & P2273 Oxygen Sensor Codes: PCM or Cat Issues?

I own a 2013 GMC Sierra 1500 with a 5.3L V8 engine and 210,000 miles. The vehicle intermittently sets diagnostic trouble codes P2271 and P2273, which relate to post-oxygen (O2) sensor performance. I've taken it to the dealership multiple times, where they consistently recommend replacing the oxygen sensors. I have already replaced the O2 sensors twice, along with the EVAP solenoid, fuel injectors, MAF sensor, and thoroughly checked for vacuum leaks, coolant leaks, and exhaust system issues. The only components not yet replaced are the catalytic converters (cats) and the Powertrain Control Module (PCM). The codes appear sporadically—sometimes setting after days or even weeks of normal driving—and then disappear without warning. During these episodes, only the post-O2 sensors read at full rich (high voltage), while the pre-O2 sensors operate normally. The issue seems to worsen during prolonged deceleration. This behavior is leading me to suspect a potential PCM fault rather than failing catalytic converters. If the cats were truly faulty, I would expect the codes to appear continuously, not intermittently. Given that the vehicle runs fine most of the time and only triggers issues under specific driving conditions (like long deceleration), I believe the root cause may lie in the PCM's ability to manage oxygen sensor feedback properly.