3 things the water pump have you replaced this at all. They do wear out. The vanes can cause cavitation and thus, not move water they way it should this is especially common on non MB water pumps. The second is the fan, not the auxilliary fan, has a clutch on it to control its speed as iti is driven directly by the engine. If the clutch wears out it might not let the fan spin enough or too fast. Thirdly you might want to get the radiator recored as this makes it like new, and will cool the water a great deal more efficiently.
hope this helps.
martin