Okay I am probably going to start an argument here period. Is the oil pressure switch from GM is it an aftermarket switch? The OEM is the way to go. Underneath the sensor is a filter and if it gets plugged the oil pressure sensor will get a lower reading. As you were saying the vehicle is new to you. So don't know what previous owner may have done for oil changes in maintenance. If you get that filter out of there or if it came out when you went to replace it get a manual oil pressure gauge and screw it right into where the sensor was. Then check the oil pressure with that gauge. The gauge on the dashboard may have a bad stepper motor and at that age and miles I would probably believe that. General Motors had a technical service bulletin out that explained the only filter to use in there would be ac Delco preferably from the dealer and the oil to use is a synthetic 5w30 weight oil with the dexos star on the front of it period. I have a 2014 chevrolet SilveradoWith a 5.3 in it and it takes 0W-20 oil. 183,000 mi and I've never had a problem with any oil pressure issues whatsoever. Let's hope that this solves your problem. Again we don't know the history of this vehicle so you might want to use it's something to clean the sludge out of the engine. I've never had anything like that fixed the problem but what happened to you. Otherwise you're going to have to look at your oil pickup tube and the O-ring that's on it. That involves dropping the oil pan and replacing the pickup tube. Good luck to you you're going to need it.
