DTC Whack-a-mole

I'm trying to sell my 2005 with 215K miles on it and I've been struggling for awhile now. It worked flawlessly until the first test ride with a buyer, when it produced a P0138 DTC, first one ever.

I had just driven through a deep puddle, which may have been the cause, but I replaced the O2 Sensor since it isn't that pricey if you DIY.

On the next test ride, the whole dashboard lit up with Misfires (P130x) Hybrid System failure P3000, and Battery failures P01a0, and block 2 low. The car had sat for almost three months after I bought my new Prime due to the winter weather, so I followed the advice for P01A0 and dismantled my battery and reconditioned the individual cells. After finding they were all about the same, I re-installed the battery.

Next test ride, I got a Cylinder 1 misfire. I swapped the 1st and 2nd ignition coils, and the problem moved to cylinder 2. Since I had replaced the spark plugs while I was waiting for parts, I thought maybe I damaged the coil somehow. Bought a new one, and installed it.

Next test ride, back to P0138. My car does consume a lot of oil, about 2 1/2 qts per oil change, non of which is leaks.

My current theory is that since the P0138 only happens at high speed, the misfires and battery problems were preventing me from reaching those speeds (since the car lapsed into limp mode). I'm tempted to just replace the catalytic convertors, but I thought I'd let others predict the success of that path.