I had a similar oil pressure issue with my 07 classic 5.3. Cured it with a new oring on the oil pickup tube. Oil pressue is its a new engine and im at 445k kms original engine.
Big Jake. As I earlier stated another tech mentioned a good way to determine if the 0ring was an issue was to overfill the oil by three quarts to cover the o-ring thereby sealing the air leak.
Now what if? What if on both trucks I worked on the problem was really the 0-ring leaking. And what if when i changed the oil the solution was not the new filter but getting enough oil back into it that the 0-ring was covered back up? What if on both trucks the oil was simply down a little?
My understanding is the 0-ring is not covered with oil when the oil is at the full mark but needs to be overfilled, by three quarts, to cover it up. But, the solution fits the circumstances so well it does makes you wonder.