Losing oil pressure at high RPM and having it come back at low RPM is a bit of a puzzle to me. There are ways it can happen, but they are a bit exotic
Do you have an oil pressure gauge AND an low oil pressure alarm?
If so, is the gauge showing low pressure AND you get an alarm?
Does the oil pressure drop quickly at 2000RPM or does it drift down slowly?
Is it stable, or does it bounce around?
Does it come back quickly when you reduce the RPM, or does it stay low?