I thought the one sec on one sec off beep was the O2 sensor. The mil lamp is showing the bad O2 as well.
I had the beep on my stbd engine a couple times in the past 4-5 trips, after starting up to move after running for a while and shutting down. It beeps, then I shut it down and restart and it's fine. This is with a new O2 sensor with maybe 25hrs on it. I have to pull codes again to be sure, but the engines have seemed to run rich since I got them, even after changing the O2 sensors.
Skooter, have you changed the hp filter? Your 3700 rpm max issue sounds more like that, and not the O2. Even with my bad, original O2 sensors, I had no issues turning 5500+