OIL PRESSURE DROPS OUT OF THE BLUE.

If someone could please help me. I have a 99
dodge ram 1500 318 5.2L. My oil pump went out
back in February and my boyfriend and I put a high
volume oil pump in cleaned every out changed the
oil every 2,000 miles and it ran fine up until june
the oil pressure drops to 0 and will jump back up
to 40. It doesnt happen everytime I drive it it rare.
But yesterday I drove it oil pressure gauge dropped
to 0 and stayed there there was a value tap in the
motor that came out of no where. I pulled into a
drove way and shut the motor up started it back up
and everything was fine no more value tap nothing
oil pressure was up to 40 I drove it home 5 mins
down the road and it was fine parked it and its
staying parked until I get this figured out.