Bill- I was just re-reading your post where you said that at 2250R's you were making 5.3K and at 3100 you were making 6.0K. For that large an increase in your RPM's you didn't gain much speed. This would indicate to me that you were trying to push the boat past it's hull speed which would definitely be working the engine hard(heat), regardless of what manufacturers recommendations are. Most likely you are overpropped a bit IMHO.
In my earlier reply I should have mentioned that I have an Autoprop, this automatically and continuously adjusts the pitch on the blades based on engine RPM and boat speed. We get the most bang (speed) for our buck (RPM) at between 22-2500 RPM and the engine is not working too hard but is still loaded up well. We can run it all the way up to 36-3700 for short periods, or run it continuously at 30-3200 but the increase in boat speed doesn't warrant it. 15 years on the engine, couple thousand hours and it's running just like when it was new (I hope saying that doesn't jinx it :-)) John
SV Laurie Anne
1988 Brewer 40 Pilothouse