low oil pressure

So I gather it is not knocking or making any noise? If all is good there, There is a screen type basket under the oil pressure sending unit that has to be fished out and cleaned. They get full of crap not allowing the oil pressure sending unit to read properly.

did you perform an oil pressure test with a gauge, if is ok then you replace the oil sender, if doesn't fix it may need a cluster, repair

The cluster sounds like it's probably the culprit. I have a 2004 and there was a recall for the instrument clusters, but you're in the same boat as me. Too many miles for Chevy to honor the recall. I've got 7 gauges and only the Speedometer and Voltage work properly.

My 2005 2500HD has a 6.0 and about 177k and the oil pressure keeps dropping but then goes back to normal and it tends to do it more when I on a gravel rd with an incline but is doing it more now

Cheers to the answer about screen under sensor, as old sensor showed pegged, new sensor only at 10 with dash warning... That said, the reason I am confident is because I sent cluster to Turn Electronics in AZ and they replaced all stepper motors in cluster, that were all pegged, for 3 years. So definitely explore both options.