I have a 1980 Pontiac Firebird. It has a 301 that was just rebuilt but this issue was going on before the rebuild. It was kept in a garage with 30 other cars in a trust for years. I have replaced or rebuilt most every thing on the car. I have had an issue with the electric oil pressure gauge. It will show about 65 pounds of pressure when I start it up and go down a bit when its hot. The issue is that while driving the needle will swing wildly from 0 to 80 back and forth so fast its hard to see and the gauge will make a clicking sound. Then it will go back to normal. I replaced the oil sending unit and this did nothing. I removed the gauge cluster and put in a new circuit printed board and it still did nothing to solve the issue. I am not sure what to do next.