I'm sticking with fuel cut. You have everything to support that theory. I couldn't tell you why you didn't get it before when you were running 23psi. The stock fpr should have been getting overrun past 18-20psi on it. That's not concrete though as every motor is different.
Wait for your afpr to arrive and after you've installed it. Remember the fuel pressure should be at 43.5psi. I hope you bought a gauge too.

As for your ECU...check the plug wiring and any wiring that may have been connected to any of the ECU's wires. Something was cut or altered causing this situation. The ECU doesn't have a backup battery or memory battery like a home computer does and it will naturally not save any settings as if you removed the battery terminals. That's crappy troubleshooting, I know, but it's very hard to troubleshoot that without knowing what was done to cause this. I can tell you all day long to check the wiring or fuses or fusible links but if you can backtrack to when this first started, it would be that much better and the recommended procedure...back tracking that is.