Older points ignition vehicles used a primary ballast resistor to keep the coil from popping with the key ON, engine not running.

Electronic ignitions have the choice of not driving the coil except when the engine is running, using a ballast wire/resistor like the old days, OR using active current limiting when there is no RPM signal.

Anyone know what Ford's PCM does?

You said the ECU was changed, but was the PCM changed?
If you leave the key on, but the engine isn't running - after say 5 mins are your coilpacks HOT?

 

Did you figure out this issue? I have a similar issue.

 

Guess I'll add my 97 ranger to this problem. Been through 3 oem coil packs. The original, truck was running good, then dropped power and running rough. Couple miles later stalled, wouldn't start. At first I thought fuel pump because there was no fuel pressure. come to find out, the #19 25amp fuse in box on the side of the dash was blown. I had 2 other used good oem coils and truck has killed those and blown the fuse. Every time the coil cracks around the middle coil. Ohm test confirms middle coil is dead. And 2 of them have ozzed some white substance out the bottom crack. I put in a blue streak and truck ran fine for 50 or so then same symptom, lost power then quit, blew the fuse. This one didn't crack like the oem ones. I did the ohm test on primary and secondary and checked out okay. I ohmed the wires from the plug in to the pcm and those all were .06-.11. I have a 95 4.0 and checked those wires and similar readings. I do have another pcm in a 97 b4000 that also is a 4l and 5sp. guess I will try that.

 

A possibility might be poorly seated plug wires. Spark jumping the gap in the coil pack towers can cause heat that causes failure. Just a guess. I'd make sure I had good wires firmly seated next time. The fuse probably blows after the coil pack fails internally and shorts to ground. Good luck.