Oilpressure dial fluctuating

[BoatService]

Hi.
Have a 4.3 mercruiser EFI.
The analog oilpressure gage has started to show lower pressures the faster I drive. The dial is also vibrating/shaking as the pressure gage drops. Best pressure on idle. Just changed oil and filter, the issue was present before the change.
Where do I start to look for the problem.
Kr,
Max

 

[makomark]

Use a known good mechanical gauge to see what the oil pressure is really doing as RPM varies...

where to start will be driven by what the problem is...