Agreed with those above, especially the part of going with the original oil pressure sender/sensor, I bought a BWD one and had issues similar to what you are describing, once I replaced it with the OE AC Delco sender/sensor, it was back to the way it was working before.
I see two sender'* listed on RockAuto, and I believe the original is ACDELCO Part # D8048, that one is delayed due to being in another warehouse, that makes me think it is most likely the original one, but get a look at the one in there now, and try to see exactly what it looks like, I'll attach pics of each sender with part numbers.
The one mentioned above is harder to find, so if that is the one you need you'll have to order it from RockAuto.
Here is the D8048 Sender.
And below is the 213-1650 Sender.