The random misfires [without individual codes] are so mild that the only way is to substitute one at a time for a week each until you find the culprits.

Make sure you have FRESH primary O2 sensors [every 60k interval] as these are where the misfire data comes from to feed ecu logic.

Years ago when there was only one coil and points and distributer......coils, points, cap and rotor along with wires were replaced every 30k.

We have gotten so spoiled with modern improvements.

I drove it about 3 hours at highway speed and it quit missing

I started it the next day and it was missing again

Less air, less fuel, less spark, dirty plugs, dirty intake valves, dirty piston crowns. Poor seal piston rings when engine is cold until warm up. Multi dozens of things that show up as engine ages especially when not perfectly maintained.

With the proper advanced test equipment you can listen to exhaust pulses and syncro them to firing order and gauge which pulse [sound] is ok and which is a misfire or even a partial misfire.

Usually beyond the scope of dealership test equipment.

The whole point of this is to still get a spark to the cylinder through the suspect coil pack, but be able to use an inductive timing light on the plug wire (coil pack extension cord, so to speak) and verify that that individual cylinder is the one that is skipping.

Notes:

1) As previously stated, the ECU will tell you which cylinder is misfiring, so it's somewhat redundant, though it gives you verification that it's definitely spark not making it to the cylinder. Coil packs are also more likely to miss under engine load, which is easy to detect with a hand on the timing light and a hand on the throttle cable.

2) All coil packs should be replaced at once. When one goes bad the others are likely to follow. It's the same as the suspension comparison--you wouldn't (or shouldn't) replace one strut.

This is a new set of OEM coils for $189.00, they have multiple sets, reputable dealer. I'll test themand post the results.

The only way to test them is very unreliable. The best thing to is to replace them all.

I have been driving on a bad injector for 2 years. Buy the cheap NGK's, and they'll produce less spark, and as a side effect it will put a lower draw on your injectors, and you'll barely notice a misfire, unless its really bad already.