Misfire ignition coils

Sounds like the issue is not the coil. What codes do you have when it is missing?
If it is a random multiple miss P0300 code and not a specific cylinder code (like P0302 for a number two mis) you will want to check for a vacuum leak and check the fuel pressure. Both are common causes of misfires because they cause lean conditions in the cylinders.

Fuel pump wise-
Resistance - 11.4-12.6 ohms.
Pressure is variable based on demand 39-65 psi.
It is controlled by a pressure sensor and the fuel pump control module.

That is good you know at least the pump should be okay, but if the module is faulty you still would not have the correct pressure, same if the pressure sensor tells the PCM the incorrect pressure.
The module controls the pressure using pulse width modulation. Basically turns it on/off really fast. The more it is on the higher the fuel pressure.

What codes have you pulled from the PCM?

Powertrain Control Module. If you have misfires it will store various codes that can help pinpoint the problem.

Start by swapping that coil with it's neighbor. Erase the code. Then see if you still get a P0305 or if the code changes to match where you put the coil. If it moves it indicates a bad coil. If it doesn't move then it's a bad plug, bad injector, low compression or a wiring issue.

Have you changed the plugs at all?

The common code found with the Lincoln/Thunderbird with the 3.9 is a P0300 which is random misfires. That is caused by oil or water getting into the coil well areas and causing problems. As you only have a single cylinder miss and not a multiple misfire it is easier to move a couple parts to determine if they are the cause.

Now if you pull the #5 coil and it's got oil or water in the plug well then you will probably be doing valve cover gaskets to stop the oil. But you said you changed the coils before with no mention of oil or water.

Those are the common reasons for the misfires. In your case it's a single cylinder and no oil or water.

If the miss is only at the one cylinder it will depend on what the actual problem is.
I have coils like those with over 250,000 miles and they are original.

We just need to determine what the actual problem is. A single cylinfer miss is a lot easier than the multiple random ones that engine normally gets.