99 115 yamaha overheat

[halibutguide]

I have a 115 hp Yamaha outboard. At idle and low rpms say under 2400 everything seems fine but on step and 3000 rpm or more I get what I believe is an overheat alarm. The eng goes into guardian mode, I put into neutral after about 30 to 40 sec the alarm goes out and I can get back on step. From the time I get on step till the alarm sounds will very from 2 min to 4 or 5 min depending on how hard I run it. I have replaced the t-stat, water pump, and have checked the popit valve. I isolated the temp sensors with no effect the alarm still came on. This is a 1999 and does not have a remote oil delivery sys or fuel alarms. Any suggestions on where I should look next?: