RPM change when boat pitches

[Skipper]

Almost all inboard motor mounted at an angle down towards the stern. If you oil level is a little high there might not be any problem if the sea is flat. But when the boat pitches stern down, the oil level stays level thus rises against the aft cylinder. The oil foams and rpm drops.

Hmmm. Interesting. I think Ron said something like this too.
When the RPM drops, it does sound more like it's coming under load, and not just a throttle reduction.

Although, I keep the oil a smidgeon under the full mark.