Well the first thing i would do is get a test gage and remove the sending unit on the engine, and test the oil pressure there and see if the readings are the same. if they are the same, it could be a number of issue's, clogged oil pick-up screen in the pan, oil pump is starting to fail, crank or cam journals are worn, first thing to do is verify the oil pressure by testing it, you can buy these gages at any auto parts store