Sounds real similar to my '55 sedan I drove in High School. I had used a pan that had the baffle removed (seem to remember it was for a boat or something) Every time I would get on the brakes hard the oil pressure would drop way down, then come back up. Oil was rushing to the front of the pan and starving the pump. I drove it like that till I was able to find another pan. Maybe something wrong with your baffle or pickup?
