Fluctuating Oil Pressure

[Kerch]

I posted earlier about changing the oil filter mounting bracket on my sister-in-law's 2000 Avenger.
I finally changed it this morning and now she said that her oil pressure is fluctuating.
It actually varies with the speed of the car. The gauge is usually about half way driving about 45mph.
Towards the high end of the guage there are 2 marks, when the speed is about 60-70mph the needle is almost to the 1st mark.

The Haynes manual doesn't say anything about HIGH pressure,just LOW pressure.
I thought maybe it was the oil pressure sending unit but there are no dealers open and it's a dealer part.

Also, on the oil filter bracket that I changed, the oil pressure sending unit is mounted on it but there is another device there also.
It's a brass cylinder about 3 inches long and about 2-3 inches in diameter with a connector that slides onto the contact on the end. Does anyone know what this is? There were a few guys at Autozone guessing that it might be a sensor to the fuel pump that actually shuts the fuel pump off when the pressure drops out????


Anyone have any advice or suggestions?
I appreciate any and all suggestions or help anyone has to offer.

Thanks,
Kerch