I have been baffled by my sudden low pressure issue. I had an oil change, had GREAT pressure for about 1200 miles, then BAM overnight low pressure. I literally went from GREAT pressure to "Wth?" pressure. Nothing drastic, but low enough to concern me. I replaced the oil pressure sending unit. Nothing. Checked the pressure with a mech gauge: low. Well crap, either a bad pump or worse, bad bearings. Well today, for whatever reason, I decided to buy a new oil filter and change the old one out. The old filter was a PureOne, good brand right? Replaced it with an STP filter. Guess what? Oil pressure is back to what it was. I was shocked. I'm gettin ready to contact Puralator now to see what happened. Moral of the story: even the best of the smallest thing can cause a big problem. Always start with the smallest/cheapest part, and work your way up; even if it is a great brand part.