overheat alarm at high rpms only

[paintcatter]

New to forum so if this has been asked before please just redirect me. I have a 2002 90 hp 2 stroke merc. I got the overheat buzzer the other day on my way to the dock. As soon as alarm sounded I cut the rpms down and alarm stopped. Cruised around at lower rpms no alarm. Back to 5000 rpms alarm sounds. Replaced impeller and thermostat. Same deal back on the water. Felt the discharge water and it was cool. Spritzed some water at various spots on the block and got no sizzle or quick evaporation. I get the feeling this could be electrical or lack of intake at high speed. I have not observed tell tale pressure being less at high speed however. Thanks in advance for your help

 

[enginepower]

Have you changed anything recently like increase the height of your motor? My motor has plugs in the 2 top water intake holes because it's high enough on fast plane that it would suck air into it. Do you premix your oil or rely on the injection system?

 

[paintcatter]

I have owned the boat/motor since new. Nothing has changed. Alarm came out of the blue a couple weeks ago. I really don't think the motor is getting hot. No sensors or regulators have ever been changed. I wonder if it could be that? I am on oil injection but the oil alarm is not the alarm I am getting it's the overheat alarm