Cummins ? ISB ( 5.9) or ISC ( 8.3)?
Many members, with your vintage coach and the ISC report a change up when Cummins works to repair the issue .
Change involves replacing the single oil pressure sending unit ; that signals the ECM and controls the dash gauge, to an installation of two senders, with a wiring change, so one reports to the ECM and the second controls the dash.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.