My experience with low oil pressure is that the oil pumps rarely wear out and are not able to deliver their rated capacity...In high mileage engines, this situation usually happens because of worn main bearings and connecting rod bearings let the oil run out too fast and the pump just can't keep the hot oil flowing with enough capacity to prevent the oil pressure from going low.....your bearings should not be that worn especially considering the relatvely low mileage you have on your engine (unless it has been abused..ie ran low on oil, filter not changed for an extended time,... anything to starve the bearings of oil or feed them dirty, unfiltered oil) You should try a straight weight oil (SAE 40 or 50) to see if that helps...The only other thing is that your oil pickup screen may be partially plugged...no one has put a foreign substance in your motor like sugar or something....have they?