My Kia Sedona has over 200,000 miles. It recently now has begun to overheat at speeds over 65 or when climbing hills and under strain. The temp guage goes up, but not leaks from radiator, hoses, etc. the thermostat was replaced, but did not resolve problem. It does not overheat at low speeds even in traffic. Power loss is noticiable at higher speeds and on hills which may or may not be related. Could it be the water pump? It has never been replaced. Thought it may be bad catalytic converter, but do not hear any rumbling when engine running, but maybe problem? Car's heater works good and helps keep the temp guage down...but not comfortable in SC in August!