hello
I have done a lot of troubleshooting around this issue, as I had the same problem.
Check that the radiator (water) is functioning ok and replace with new.
You may want to replace the clutch fan in case it is broken, although it plays very little role in speeds above 80km/h.
My car had the above two issues.
The radiator after 10+ years had only a 60% functioning area.
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