As swapping the EGR valve has made no difference, I would be inclined to clean the original valve thoroughly and replace it. A stuck EGR is a very common fault on these, and a jammed shut EGR can throw up spurious fault codes and few other symptoms, rather than the jerking/stalling symptoms which are normally experienced without putting the EML on. That said, the more typical faults seen are "insufficient lift" or "sensor circuit" faults. The actual valves rarely fail completely.
The valve pintle is sprung quite strongly to hold it shut, but the important thing is that it moves freely and smoothly with moderate force. To check this, you will need some sort of implement to carefully lift the pintle from the seat so you can get a purchase on it.
When cleaning, make sure you douse it in carb cleaner, leave it upside down for a while to soften the deposits, exercise the pintle a bit to clean out the carbon around the shaft, then flush again with carb cleaner - that's where the problems normally lie.
Obviously, a new EGR valve would eliminate it as the cause, but I appreciate the cost - you can get a pattern part cheaper, but you are still into 3 figures. A known working EGR valve would be would be the next best option, but a clean item from a scrapped car is normally a sensible option.
The odd thing for me here is that the fault appears to be exactly the same with the replacement valve, and jamming shut is not the most common mode of failure. If the pintle on the valve is clean and moving freely, then I would start thinking about electrical problems, rather than mechanical. I don't think that the loom is known to give any particular problems, not like the known issues you find with VWs or Renaults.