I had various misfire codes and hesitation/stumbling on my 1999 SVT. I replaced plugs and wires (Autolite APP764 and Ford Racing wires) and problem still occurred. At that point I looked at the running engine in the dark and saw arcing from the new wires to metal and each other. I moved the arcing locations further from where they arc to and saw a HUGE difference. I still have very slight stumbling occaisionally (tolerable though) and plan to do more investigation when it warms up outside. Hope this helps.
