I have a 2006 1500 Silverado w/ 189000 miles. Since about 150k I have had very low oil pressure on start up. Low Oil Pressure alert going off. Once I drive for about 20 min and get everything warmed up my oil pressure holds normal with no drop at all. This is only an idle oil pressure problem. If I take off and drive it holds at about 40 lbs....but when I stop and idle it goes back down. Or I can just idle at a higher rpm and it holds.
I did use vmax 10/30 and just switched to penzoil high mileage. It seems to not be near as bad with the new oil. It is 10/30 as well.
It does not matter if it is summer or winter when doing this, it just does not take near as long in the summer time to stop setting off the Low Oil Pressure alert.
One other thing, If I am sitting on an incline it does it worse. If the truck is declined it does not do it as bad. And this is when oil levels are prefect, so I know its not a low oil situation.