Geez the list of what it could be is long.
Is the fan belt on tight as a slipping belt will cause the car to overheat at speed.
Is the water pump OK, if the blades are rusted as the engine spins faster it cannot pump water?
Is the thermostat opening all the way, as the engine speed increases you need the thermostat to open far enough to allow water through.
Is the bottom radiator hose with a spring inside? As the water pump draws water the hose can collapse and restrict flow.
Is your radiators air passage clear, no rubbish blocking air flow?
Is you radiator blocked internally?
Is your water level dropping?
Is your cooling system holding pressure?
Is your oil turning milky white, water level dropping and maybe running rough?
Id start with checking the belt tension, replace the thermostat, maybe remove the radiator and reverse flush it (internally and externally) for a start.