My Focus is overheating.  The temperature gauge sticks at normal when driving around town <40mph, but when exceeding 60mph ish or going up a steep hill the temp shoots up into the red, stays there for a while, then once the car has backed off, it will return to normal just as fast.  I am getting hot air out of the blowers, but the radiator is cold to the touch after driving.  The fan works perfectly and the water pump is only 40k miles old.  The car has gone into limp mode in the past due to extended high temp (nowhere for me to pull over).  The problem started at around 120k miles so I dont think it is technical service bulletin NO.005/2001
I have read other threads with similar problems and followed them.

I have replaced:  Thermostat, Heating matrix, Radiator.
I have also used a vacuum purge and refill kit to refill the coolant to negate air locks.

when I read the first paragraph it sounded to me like a blocked radiator (silted up) but I see you have replaced the radiator.  I remember reading on one of these ford owners club forums (can't remember which car) about someone who had cooling problems and it turned out to the a faulty water pump, the impeller can broken off so was not going round with the shaft. It might not have been same car/engine type. I don't know if it is possible to tell if the impeller is working without removing pump - eg. by removing a particular hose somewhere and see it the coolant actually pumps out as opposed to just running out.

I had this problem for a long time. It took a trained pro a couple of hours to completely remove the air lock in mine. These engines are a nightmare to bleed, and he was using a vacuum refill. 

I had put in an aftermarket thermostat.  I had tested the thermostat I bought and it was working fine, but it failed between when I tested it and when I was bleeding up the car.

He changed it for a proper ford one and he said it bled up nicely.