My 2000 focus is overheating when driving fast (40+mph). Its OK when driving slow or idle. I have replaced the following:
1. Radiator
2. Thermostat
3. cylinder head temp sensor
4. timing belt
5. Water pump

The mechanic is 100% certain its not a head gasget issue (he said "you would see coolant in the oil, compression would be effected, oil in the coolant, coolant would be bubbling in the reservoir etc etc ")
There is no sign of a coolant leak anywhere.

When I run Self Diagnostics Mode no DTC codes appear. I even reset the computer!

I checked the two hoses in/out of the radiator and they are at the same temp (after the engine is left idle for a while)

Anyone have any ideas on what it might be?