Have you checked the pickup coil gap? That's been reported to cause a similar misfiring problem. They've reset the spec to .8mm on that gap. Have you swapped coils to see if the problem travels with the coil? After following several threads that report similar problems these seem to be the most common failures...too big a gap, intermittent pickup coil (heat generated), bad igniton coil and lastly followed by the dreaded blown ignitor.
