For the past week, my wife's 2012 Tahoe with 94k oil pressure has been very up and down. At 2500 rpm or so, it would run close to 40 psi but drop back to about 30 psi. At idle, about 18 psi. Running between 1000 and 1500, it would level out at about 20/25 psi. No lifter noise, knocking, etc. Researching Youtube, there seemed to be 3 or 4 possible fixes. Oil pressure switch/sensor or screen filter needed cleaning. O-ring on oil pickup tube on oil pump or by pass plunger on oil pump. Was planning on taking it to a shop next Tues. after New Year. Stopped by a dealer and the service guy didn't have a clue. Said they would have to tear it down and had no idea what the cost would be. Decided that if it was the screen, maybe changing the oil might clean it enough to see if that might be it. Readout on DIC indicated it there was about 10% left on oil mileage. Eureka! The oil changed brought the oil pressure back to normal. Stretched my arm patting myself on the back and hopefully saving a few bucks. Makes me wonder if GM programed it to fluctuate to get your attention. I understand that if you loose all the pressure, red lights, etc. will come on. I did not have any warnings other than the gauge fluctuating. 
