FWIW, after 18 months of living with similar symptoms, replacing wires, plugs, MAF, and cleaning entire intake, EGR pathways, and Cam Position Sensor, I just went to the Ford dealer, picked up the Motorcraft OEM plugs, and installed them this evening.
Result? The stumbling (hesitation, bucking, etc) that I have had at high load/low RPM (<3k) is completely gone. It remains to be seen if this fixes the problem long term, but after about 15 miles of various driving (accelerating from 1k RPM in 5th, WOT up hill) I have had no problems at all. I would recommend this to anyone that is having this problem and does not have the OEM plugs. They really do look different from the Bosch and Autolites that I had tried before. For $25, can you really go wrong?
For reference, I have a '95 SE Duratec with ~125k miles on it.
Geoff
