i have a 2008 GMC Acadia. My oil pressure alarm is ringing.

You need to have the oil pressure checked mechanically before going any further. It's possible you actually have low oil pressure.Use this link to find a good shop near you. https://repairpal.com/repair-shops Alex

LOOK at oil pressure gauge - what's it telling you? .. IF audible warning is on - oil pressure gauge reading should be extremely low! Professional scan test - instrument cluster live data plus gauge functional test can be performed. I find it difficult to imagine why a GM dealer would not have performed all procedures that's posted here ...