I'm not saying this is your cause but one you might want to rule out. For several years my car showed low
oil pressure and was very unresponsive to RPM gains. It would always seem to fade. I was always chasing this and changing that to resolve it. One day I had what is called a lightbulb moment and decided to run a bigger gauge wire with new crimp on teminals from the sender to the gauge. Bingo! I had great pressure and now the pressure responded to RPM changes. I ended up swithing to a mech. gauge anyway but if your running elect. you might double check your wiring. Good luck!
John