Low oil pressure, again

[ksmech11]

Got a 2011 Prostar. ISX 871, Just changed oil and filter. Replaced air filter and crankcase filter. Cleaned and rebuilt doser. Performed egr tune up. Ran regen. during regen oil psi stayed at about 32 psi. After regen was complete the psi went to 20. Running Napa oil filter and FS 1540 oil. My boss thinks it needs an oil pump. I heard that many guys have changed the pump but low oil psi returns. I really am trying to avoid having the international dealership try to say it needs an inframe. Only 458k on it. Im gonna get a manual gauge and confirm the oil pressure. Insite showed what the gauge shows. Anything i may have missed or need to check?