Yo Scott :
couple o things :

I never bother to ohm check plug wires anymore.
If they are very old, like over 5 years, they are suspect.
if they are cheap, like not bosch or german, they are suspect.
i have worked on cars for dozens of hours only to have the plug wires be
the problem in the end.

Here's a simple little spark plug wire test.
find some total darkenss and watch the plug wires
while the engine is running, looking for little sparks leaking out here
and there.  Doesn't always work, but sometimes it does, and it is a real
simple test.

Another test, is spray a fine mist of water on the plug wires while it is
running.  If that makes it stumble,
- spark plug wires !
and, how big are the plug gaps ? if those are worn huge it will be harder
for the spark to jump that gap, making it more likely that the ign
voltage will leak out somewhere prior to the plugs.

But, I don't think that is your problem.
did you look at the plugs, hoping to see one wet or dark or different
looking than the others ?

Have you checked in the FUEL filter for rust partricles, water, tiny
metal partricles ?

It would be very nice to operate the injectors out of the engine to see
their spray pattern ( this is a little dangerous and not a normal at-home
kind of thing to
do ).

The bentley book tells some things but is really not that back-yard
friendly.  They do tell about the above test.

Try to catch it running rough and isolate it to a cylinder not producing
power, if you can.
If you get to it is running rough because one particular cylinder is not
firing / spraying / producing power that will be half the battle.

You could even have, say, a poor connection at one injector, try wiggling
the injector wires gently while it is running, to see if you can find a
poor connection.

I use carb spray cleaner to look for vacuum leaks, not
WD-40.

How about faulty fuel pressure regulator ?
it happens, altho not usually intermittantly.

 anyway, a few thoughts.

  Scott