65 PSI is excellant. The OP relief valve & spring are functioning as intented.
Squeeze and clean the connector to the OP sender unit, as well as cleaning the OP sending unit spade terminal et. al., this sounds like a dirty connection responding to a vibration frequency (rpm).
Check that the engine to frame ground strap (bridging the driver's side motor mount) is clean (no paint) and is well connected.
Sometimes the OP sending unit will fail. Replace the OP sending unit.
Excess oil pressure (on the dash guage) is not a good thing. The oil pressure passages that feed the bearings in the block are finite in size, and thus are limited in the volume (amount) of oil that can be feed to the bearings. Increasing the oil pressure past the limit of the passages to transport that oil results in the excess oil volume produced by the pump being bypassed through the pressure relief valve back into the oil pan, resulting in foaming of the oil and horsepower loss due to over driving the oil pump. Additionally, the cam/oil pump drive gears are subjected to unneccessary extra stress, resulting in unneccessary wear and heat production.
Check all of the electrical connections from the OP sending unit to the dash guage, polish everything, and make sure all of the electrical connections are tight.
coupeguy