GM's first step for low oil pressure is to change the oil!
Cut open the old filter and see if it is full of stuff. The DIC comes on at 9 PSI. You only need 13 PSI at idle as I recall. Shifting into gear or reverse to drive will cause a sudden oil pressure drop of ~3 PSI.
Last time I had this issue my oil was 2 quarts high from biodiesel contamination and it was thinning out the oil on the 2008. Thus a big reason GM says to change the oil first. An oil sample can also tell you if coolant is wiping a bearing etc.
Oil pressure switches/sensors are famous for failing. You only need to test there for pressure with a mech gauge.