[77newell]

I had something similar happen recently on my 77 coach with 6V92. In my case the pressure would not pick up to "normal" levels after driving for awhile and then slowing to idle and accelerating. It was reading about 20 PSI low at speed and almost zero when at idle. And then sometimes it would just spontaneously pick up. Since I have a pressure gauge right next to the transmitter I checked it against the panel gauge and noted that the panel was reading low. I checked the ground of the transmitter it was OK and ultimately concluded it was the transmitter.

Can't say this is your situation. If the gauge's readings are jumping up and down it is most likely an electrical problem. I say that only because whenever I've had a mechanical failure the pressure went down and stayed down. An oil pump may wear and lower pressure very slowly but if the drive shaft breaks the pressure will suddenly drop and in my experience stay there literally at or very near zero as the tub ends at the breakage point rub each other into oblivion. Unless your engine was full of sludge the filter wouldn't have plugged 500 miles into a oil change, but if it did plug the pressure would drop until the bypass opened and then pressure would return to normal and behave as usual.