There are lots of people on the forum that have experienced the same thing and figured it out. Do a search on "Oil Pressure Gage" and see what comes up. I see solutions ranging from cleaning the contact for the wire to the sensor to buying an OEM sensor instead of after market. Read through some of the threads to see what others have experienced and done to correct it.

O.K. I will,, but first I unhooked the cheap oil press. gauge and hooked up one from my '68 Firebird which is top of the line took car for drive and oil press gauge did same.
So it looks like the gauge is at fault or something gauge related.

I have the same issue and have done both uim and lim I believe it to be the gauge specially when the needle flicks back and forth so fast it can't be accurate also really don't want to do main bearings