I have Mercury 50 hp 2 stroke serial #OT455207 . I have replaced the impeller and thermostat...my temperature sensor alarms at low speeds but never at high speeds. 3000+RPMs no issues, slow cruise alarm....speed up alarm goes off. Water stream is fair, better at high speeds. Flushed it, blown air no restrictions. its on a pontoon (26"tubes) and I'm starting to think the engine does not sit deep enough and the wake is creating the problem at low speeds. bad sensor???