7.3 Lack of Oil Psi

Guys i could us some help. A guy at my job has a 95 E350 with 2 psi of oil pressure @ hot idle and 30 psi at 3000 rpm hot. He just inspected the oil pump and replaced it anyway although it was in spec. That didn't fix a thing. SO now he and im not sure ware to go next . I though maybe pull the front cover and look for any kind of aeration check valves or something like that and take it from there. The engine has about 137000 miles and is a fleet school bus . It has had an oil change at 5000 miles since it was New. I could use some ideas Please . Ohh we also over filled the engine with 4 qts and lifted the rear end up on a jack to see if oil psi would come back thinking maybe a pick up problem but it didn't do a thing to help.