40 psi oil pressure - 2000 GMC Sierra

Usually two reasons why oil pressure drops over time,worn engine parts,old oil.Try an oil change with new filter I sometimes use an additive like Restore.Over time the oil will become thinner and less viscous leading to a drop in oil pressure.

A leaking filter and oil pressure switch would cause the lack of oil pressure. Does the oil light work and does it go out now you have changed these parts. It only needs approx 8 psi to put the light out, the engine should run at approx 40 psi at 2000 rpm.

Did you verify oil pressure with an oil pressure gauge besides the one on the instrument cluster?

Wild guess of 40 to 60 psi at highest, and more like 10 at idle.

When the engine is idling, the oil pressure is reduced. At fast idle (such as highway speed) it in increases. This is considered normal. If it goes higher than 80 or lower than 40...have it checked out.

Increase the viscocity of your oil. If you're using 10W30, go to 10W40. If you're using 10W40 switch to 20W50. Don't use single weight oil.

try another earth cable ?? straight to engine and chassis

yes it might work if u flush it, give it a try

either the oil pressure sender is defective or the pressure relief ball valve in the oil pump is sticking, my money would be on the oil pump pressure relief valve ball sticking.

30-40 psi of oil pressure is fine for many vehicles including your GMC. I am assuming that the truck has more than 100,000 miles on it and still has the original engine in it. By rule of thumb you only need 10 psi per 1000 rpms in a typical street driven engine to give adequate oil pressure to keep the bearings from oil starvation. The oil pressure is typically higher when initial start up occurs because it is more viscous due to the temperature of the oil as the engines oil warms up the visconsity thins out and the oil flows more smoothly. The drop in oil pressure is a normal occurance. Above 45 is more than required for a daily driven street engine. I believe that the specs on that engine only list 30- 45 psi.