2007 International DT570 Low oil pressure issue

Hello all, hoping to find some advice here. I have a DT570 that I got as a basket case from another shop. We did an inframe on the engine from a failed cylinder. It appeared to have failed due to a piston cooling nozzle issue. The old nozzles were not there so I could not verify that. After replacing the head, pistons, liners, bearings, one injector, and the oil pump we fired it up and it ran great. It has 65PSI oil pressure at an idle cold but when the engine is up to temp the oil pressure falls to 7-10PSI. The oil pressure fluctuates 5PSI back and fourth all of the time. It has been verified by a mechanical gauge and the fluctuation and pressure are accurate. We replaced the oil pressure regulator with no change. After running it there was a leak on the front gear cover so that was resealed and while it was apart we rechecked the oil pump, pickup tube, front structure, piston cooling nozzles and anything we could get our hands or eyes on. The engine only has 110,000 miles on it as it was a remanufactured international swing engine that was installed years ago but not many miles ago. The owner is not sure if it had an oil pressure issue before it failed but I am beginning to wonder if this issue was part of the original failure. My background is extensive in heavy duty Cummins and Caterpillar on highway engines but not the Internationals so I feel a bit of a disadvantage here. Any thoughts, ideas or help would be greatly appreciated.
Thanks in advance!
BB

 

Searched before I posted and found nothing helpful. Was hoping to find someone with some good experience with these engines.

 

Oil never gets over 180, Cant find anything wrong with the cooler. Relief is new, no change after replacing it.

BB