Cam bearings can seriously rob oil pressure if they are bad. It sounds to me like you've got some clearance in there somewhere. Try running a heavier weight oil in the engine, it may save it for a little while. Or, if you want to try and save all the parts, attach a real oil pressure gauge to that thing man. The stock gauge is a piece of ****, it should only be used as a pressure or no pressure device.
Sounds like you really need to get back in there to me. Don't forget to check the rod bearings and all that stuff. Could be any number of things, but since you have swapped out the oil pump, it doesn't look good.
