I had a similar issue in my 2009 Tahoe. It would lose pressure, but if I shut it off and restarted it would come back, albeit lower than where it should be. Then after a few minutes would drop again. I changed the pressure sender and the little screen and that didn't help. So, after reading everything on this forum and seeing that people have had issues with certain oil filters causing this type of issue, I took it to Jiffy Lube and got a conventional oil change (only had 1000 miles since the previous oil change). That fixed it and now 4500 miles later not a single oil pressure issue. Never heard of oil filters being able to fail like that in all the years I have owned and worked on cars and neither has anyone else that I know. So strange.