Oil pressure loss

This is normal for it to drop slightly. As the engine heats up the oil actually thins out. It will turn from a thick molasses consistency when cold to more of a syrup on hot pancakes consistency when hot.

Also, when the RPM's are low there is less pressure in the system so it will drop. If you rev the engine it will spin the pump faster and raise the pressure. I attached the spec for your review.

Let me know if you have more questions. I'm hungry for pancakes now. :)