Ok, what you will need to do is attach a mechanical gauge in place of the sending unit and see what your actual pressure readings are at idle, and at 2500.
Let me know what the readings are.
Ok, if you are losing oil pressure then you are going to have to open this up again. You can use low pressure compressed air fed into the sending unit hole in the block to look for places where there may be excessive leakage of oil pressure........worn bearings etc.
You'll need to drop the pan again to see where the pressure may be leaking from and you may as well check the bearings while you are in there.