Okay, so I've managed to do a few things:
- changed the fuel filter and regulator with a Hengst branded one
- replaced the throttle body with a new OE (VDO/Continental) one. I found one on clearance at Rockauto so went ahead and did it.
- Did a visual boroscope inspection of both catalysts through the O2 sensor ports to see if they were clogged. Not obviously melted or anything.
Unfortunately the problem persists. It's hard to diagnose anything through INPA because the refresh rate is so low it totally hides transient issues like this one. Are there faster/better monitoring or logging options? I'm running out of things to try. I could go ahead and put a new fuel pump on since the original is probably on borrowed time and it's not that expensive or hard to do.
Will try to get the software update next week.