I have a mk5 for fiesta 1.25 petrol. The radiator was repaired about 6-8 months ago it ran smooth since, then the thermostat was replaced recently followed by a water pump due to melting cause of a stuck thermostat. Since the temp is OK until I go out of a 50 kmph zone and have to drive 80-100 then it begins to overheat, once I slow it starts cooling down to its normal temp. There is a gurgle from the heater matrix but no wet carpets or anything. Can anyone help me? 

Could be an air-lock in the cooling system somewhere? 

like Andy said could be an air lock in the system somewhere, i had a problem much the same on one of my old cars turned out there was an air lock and the thermostat housing had an air pocket in it. (bad design and not a ford but same issue would over heat and gargle from time to time but everything dry)

Fit turned out to be a coolant system flush and refill with the correct bleeding process. If you have the room, time and confidence to do it drop your coolant and do a flush and refill following any bleeding guide lines. If you dont take it to a trusted garage and ask them to do it for you 🙂