CM871 OIL PRESSURE

[untouchable]

WE ARE HAVING AN ISSUE WITH A CM871 OIL PRESSURE. AT IDLE IT IS SITTING AT 20 PSI, VERIFYED WITH MANUAL GAUGE. WE TORE AND INSPECTED ABSOLUTILY EVERYTING, NEW HEAD, BOTH CAMS, OIL PUMP. RODS AND MAINS, OIL PRESSURE SENSOR, FRONT STRUCTURE RESEALED, OIL COOLER RESEALED. STARTED AND RAN AT 45 PSI. TEST DROVE AND COOLANT TEMP WAS AT 195 OIL PRESSURE WAS 18-20.THE TRUCK HAS ALWAYS RAN 30 TO 40 PSI THEN A SUDDEN DROP AND NOW CAN NOT GET IT TO STAY WITH IN THAT RANGE. ANY HELP WOULD BE GREAT