Hello, I hope I can be of assistance.
From the description you've given it would seem the car has a misfire, given the previous repairs there is an underlying problem causing this.
Check the spark plugs, when you remove the HT leads use a torch and check in the holes where the spark plugs are located under the valve cover, look for any sign of water, this model does have concerns with water getting into the spark plug area causing misfires.
If there is water then the source needs to be checked it is either due to heavy rain which comes through the washer jet openings in the bonnet and drops on the engine or one of the core plugs between the spark plugs is leaking allowing coolant into the spark plug area. If it is rain water then fit new washer jets as the rubber gasket goes hard and allows water through. If it is coolant then the core plugs need replacing.
I would also recommend using genuine Ford parts, although slightly more expensive they are much more reliable, especially the spark plugs, some cheaper parts do have reliability concerns.
Try to confirm the problem is a misfire caused by an ignition fault, if it is then check as above.
I hope this helps but if you have more questions regarding this let me know and I'll reply as soon as I'm able to.