My op was dropping then after shutting down would start up normal slowly go down. I've had the irratic op but it's more constant now. No knocking, oil smells and looks fine and op is in range at start. Had o rings changed carbon cleaned from oil pan only thing left is oil sensor. 2005 z71 towing package. Any ideas?

 

I would change out the oil pressure sending unit. These are a pain to reach and R&R, but I did this on our 2014 Yukon after watching several YouTube videos.

If I had to do this again, I would cut away some of the plastic "sound barrier" obstructing access.
Try some of these:

This one mentions removing the plastic shield