Oil pressure gauge shows low. gauge lite comes on, no knocking..change iil pump?

It could just be the oil pressure sensor that is failing.....that is why the gauge shows low.

Has the oil pressure been tested with an external gauge to verify? You mention the sensor was replaced. Was it with a new GM sensor, or one from a parts store. I have seen many parts store sensors bad out of the box. Always remember, new means new. New doesn't mean good. I have had a customer that was certain the oil pressure was bad. I proved otherwise with an external gauge. Video of it is on YouTube listed under our streetsports1 account.