I don't think it is plug wires.

My 86 Crown Vic with 270k miles ran like a top until this winter when
it developed a miss-under-load sounding exactly like your problem.

First thing I did was put in a new set of plugs.  No change.  Problem
still there.

Having been on the original plug wires all that time, next thing I did
was put on new plug wires.  No change at all.  Problem still there.

Now I suspect the ignition module or throttle position sensor (TPS).
I'm leaning toward the TPS being the culprit, since it occurs only
when throttle is opened up.  My theory is that timing advance would
work off the signal from the TPS.  If TPS is sending an erratic signal
to the computer, the computer would do erratic timing advance,
occasionally causing cylinders to fire way before TDC, resulting in
random kick-backs under load, the exact problem I'm experiencing.

Here's another oddity:  It almost goes away on a warm 60+ degree day.
I suspect it would clear up completely on a 70+ degree day, but I
don't want to wait that long hoping the problem will fix itself.

FWIW, a similar problem was completely fixed on my 87 F150 300 6-cyl
pickup by putting new heat-sink grease between the ignition module and
distributor housing.  That might be a totally different issue though.
The deteriorating heat-sink grease problem on 80-ish 300 cid engines
was a well-known pervasive problem, even triggering a recall in
California due to accidents it caused when engines would start
misfiring severely enough to die at highway speeds (as mine did).
This problem on my 86 Crown Vic is not nearly that severe.

Maybe somone out there has had this problem and knows the soluton.

thanks!
george

Fuel filter?
Often overlooked, but essential. Will pass gas, but dirty gas. Probably no
need for additive(injector cleaner,) just motor on.

wws

It very well could be plug wires again. Make sure the air filter is
clean, change the fuel filter and clean the MAF sensor first, though.
Time and atmospheric conditions are the enemy of plug wires, not
mileage. Wires on any car are usually only good for 5-8 years, not
just Ford wires. The 4.6L in your car tends to need wires more often
than many, though. Pull the wires out of the intake and look at the
boots. Look for oil/coolant contamination or signs of arcing. If there
is liquid contamination new wires will fail quickly, you need to fix
the cause of the leak. Arcing (burn through on the boots) is often
caused by not using dielectric grease on the boots. Look for a hazy
grey spot on the side of the boot with a tiny pinhole in the center.
Look for tracking around the bottom lip of the boot.

Here's a couple of tips specific to your 4.6:
-Only use Motorcraft wires. They will burn up cheap wires very quickly
-Use standard copper or single platinum plugs, Motorcraft or NGK are
preferred. You WILL have issues if you use any Bosch spark plug in
that motor.
-Always use lots of dielectric grease on and in the spark plug boots.
-Periodically inspect and clean out the spark plug wells. Valve cover
seals often seep into the wells, ruining the boots.