You might of knocked the sensor when you where doing the intake gasket, they are quite sensitive and break pretty easily, and they are right there at the back of the block, so it's not hard to accidentally hit it. Don't trust what your gauge says, do the test I said, T-tap inline with the oil pressure sending unit and check the pressure with a manual gauge to make sure it has oil pressure. It's a simple test, it just takes time to get back there and set it up. If the oil pressure test shows you have around 20-40 psi at idle, and over 40 psi under load, then the sending unit is bad, and you should replace it. If it shows you have no oil pressure, I'd start with the oil pump, remove the oil pan and check for a clogged screen, and might as well replace the pump while you are at it. I highly doubt it's the main bearings or crank bearings, at 229k miles that engine has plenty of life left in it.