Sharing with everyone that I found the problem and I was able to eliminate the overheat problem. The previous boat owner shredded the impeller and did not do a thorough job of finding the pieces. I found chunks of impeller rubber compacted into a plastic water distribution tube about 18 inches...
Reaching out for help to diagnose a low and high rpm over heat. High overheat occurs above 3500+ rpm when at this speed for more than 3-4 minutes. Low overheat occurs at lowest idle, 600-700 rpm, when at this speed for 10+ minutes. When engine is increased to 800+ rpm the temp cools down...