[THEFERMANATOR]

1st thoughts that came to my mind was bad poppet or weak impeller. At higher rpm's the poppet is supposed to open and essentially bypass the t-stats to cool the engine down under load. It's a pressure based system, so if its not making good pressure, the poppit can't do it's job. As impellers age, they lose there pmiability, and the impellers don't stay out at higher rpm's. Stats wouldn't be a bad idea to do either. I believe you can get the omc stats to go in that engine to get stainless ones instead of the brass steel ones. A water pressure gauge is a GOOD gauge to have on one of these as it tells you right away where to look.