Thre is a plug that goes inside the oil galley near the oil filter inlet. It must be driven in an approx distance. Without this plug inplace at the correct height the symptoms you are desccribing will result. There are 2 cupped plugs located at the front of the block behind the timing chain. The other plug is located at the oil filter pickup point but it is installed above the oil pump. It is driven in approx 2 1/8 to 2 5/16 from the block surface. Without this plug at the oil pump/filter intersection the symptoms you describe will happen. Another although mesy approach would be to observe the oil coming to the valvetrain with valve covers removed and priming the engine maually with an electric drill and slowly rotating the engine to observe any internal leaks, the intake can also be removed to observe, allthough these are last resort tactics. Whatever the solution it must be fixed, the engine will 'eat itself' if this isnt resolved. You could dump in some 20W 50 to se if it helps raise the pressure, but I think there is something wrong internally, and it's not a clearance issue like to loose of bearing clearances. Good Luck