Did you prime the engine before start up?
If you are reading 80 psi at the oil sender, (right hand side, towards the back) you must have oil everywhere in the engine, are the push rods and rocker arms getting oil?
I think you are right about the relief valve in the pump. No filter is going to hold 80+ psi for very long, so I don't think I would try a third one. Try pulling the distributor and tapping on the oil pump housing, the check valve may break loose. Other then that, pull the pan and have a look. Joe
