Jerry
The C9 has two separate sending units that report oil pressure. One sending unit provides information to the dash gauge, the other unit provides information to the ECM. You are having an intermittent issue with the sending unit that provides information to the ECM. I would recommend you order a new replacement sending unit from CAT. Both sending units are located close together on the passenger side of the engine about mid way up from the bottom. They are a bit difficult to get to (you will likely have to move or remove things to get to them). Which is why I recommend you have a new one in hand before you get in there. In my case, it was the dash gauge unit that failed, but replacing either one is the same process. Good luck.
Richard