My wife has a 2007 Expedition Limited with 126k miles on it. It started to shake around 40mph a few months ago and only seemed like it would happen when trying to go up a bridge or pass a car. I thought it might be the Coil over packs and took it to a mechanic and he tested it and it showed nothing. He changed the fuel filter and put a cleaner in the gas tank and it did feel better for a few weeks until the shaking started to come back. Well the check engine light came on and I tested it at autozone and it said Misfire cylinder #4. THen the light cleared. So now I dont know if its the sparkplug or the coil over pack. She just called me while Im at work and said as she was backing into the drive way it started to shake really bad and make a loud spudder noise but she said it was hard to explain the sound. I never felt or heard this while going to slow into a drive way. What could it be? its driving me crazy at work not knowing if the motor is shot or not.

Cliffs
-2007 expedition
-126k miles
-Shakes and spudders at 40mph when passing/going up hill
-engine light showing misfire on cylinder #4
- tonight it started to shake really bad and make a loud noise just backing into the drive way.