I tested the resistance on the secondary side of the coil pack. The manual tells me it needs to be between 6K-10k ohms. I am getting a reading of about 15k ohms but it is on all four secondaries. (5.0 L V8). It seems odd that the values would be thsis far off on all of them at once. Like it is somehow wearing out slowly versus a failure on one coil. Is this how coil packs go bad? slowly. Thnaks.

 

In my opinion, replace them. If they are not within factory spec, they are probably effecting performance.
About a year ago I bought Accel ignition coils. My factory coils were within tolerance, but I replaced them anyway. I did notice a slight gain in performance over stock. But maybe that was a sign that my factory coils were indeed, going bad. Or maybe they are better. Anyones guess. Good luck.