Same thing happened to my brothers 496 but it started out with 60 psi then dropped down to about 15 psi. We messed around with the fittings the gauge. Finally we just dropped the oil and put Rotella 15w-40 started it back up and back to normal. We thought we where going to pull the engine too until we did that. The oil almost looked a little milky maybe from all the assembly lube I don't know. Still good oil pressure to this day. Good luck