Try pulling the Fuel Injection Pressure Regulator vaccum line, it should be dry, if you see some gas its bad, that could be the problem, my brother in laws 2001 lesabre has the same problem, and after doing a tune up and lots of other things, we finally figured it was the Fuel Injection Pressure Regulator was leaking

Spark plugs look good and all pretty much like this one.

Upon reinstalling the plugs I noticed this burned insulator on the #6 plug. Sneaky little bastard.

So Changed the plug, gave it a sea foam, and it'* purring like a kitten. Now I just need to fix the possessed seat heater.

Ahh, that black spot could be a carbon trace, and arching to ground. Otherwise the plug looks good.

UPDATE: I replaced the ICM and coils. ICM is by BDW and the coils are BDW select. This fixed the highway stuttering "vibration" issue and netted 8MPG. I took a 100mi round trip shakedown drive to Palm Springs after the instillation and noticed the average MPG for the trip reading 29.6. That was with a headwind of the rainstorm moving in and some hills.

Good mileage. A strong spark makes a big difference.

I'm looking at changing out the champions with motorcraft, or pulsar if I get rich. I imagine the new coils would love the pulsars.