39 pickup oil pressure fluctuation

[Willit Stop]

I had a similar problem.My pump was assembled incorrectly and there was a gap between the tin can and the pump body.An easy way to check if this is your problem is to park on a steep incline(front end up) and check the gauge.You should have steady pressure.Next,turn it around(rear end up)and check the gauge again.If there is no,or low,pressure,you might have the same problem.Hopefully,it's something simple because pulling the pan isn't fun.
Good luck.