Temperature falls with speed

[Ged Robinson]

Hi has anyone come across the issue of temperature gauge dropping and heater looses heat 90 to around 50 when travelling over 60 mph? Ive changed the thermostat, CTS sensors top and bottom, flushed the engine block and radiator but it still does it. Just don't want to be cooking the engine, the heat must be going somewhere. Reduce speed and temperature rises, heater blows really hot ... got me beat !

Thanks Ged.