I'm sure this has been beaten to death all over here but here goes. I've been out of the dealership for almost 20 years as I left for benefits at the post office. ase master when I left.
Recently purchased a 2010 sierra 4wd 5.3 lc9. Had afm tuned out the 2nd day I had it. Does not use a drop of oil and have taken it on 3 -1000 mile trips. I've put about 9k miles since I purchased. oil pressure would sit above 20 hot idle in gear. Now it is dropping down to about 10-15. The warning light is not on yet.
Put new gm sensor and replaced the screen. The screen looked new when I pulled it out. Cheated and took a manual reading at the oil port on side of the block. Hot idle it shows 25 there.
Cold start with 40 degrees outside it has a slight 1-second hesitation before jumping up to just past the 0 on 40. 10 miles later I am at about 10-15 in gear.
no noise, runs great, have ran 5w30 syn both Mobil1 and QS.. 3 different brands of filters with no improvement. (I truly don't see how any filter is really going to vary oil pressure unless plugged and then would go into bypass anyway)
Don't really see oring as an issue but going to drop the pan and replace the pressure relief valve. And then probably put a 10355hv melling pump in since I am halfway there anyway.