If you have a recurring misfire, let's look at the things you
have not changed: the combustion chamber: a
compression test may be in order. Is there oil, gasoline, or
soot on the spark plug when it begins to misfire? the fuel
injector for that cylinder: could it be dribbling instead of
spraying and causing that cylinder to load up? Keep in mind
that those coil packs fire two cylinders at a time. Could the
other plug or wire have problem that's keeping this one
from performing properly? If you short one - the other
probably won't fire right either. Just some thoughts off of
the top of my head. I haven't seen this concern much and
usually it's a plug wire arcing to the exhaust manifold.