I have a 2004 Ford Excursion 4x4 with the 6.0L diesel and 213,000 miles. Yesterday morning I started it up and it idled really rough. The whole vehicle was shaking, almost as if it was misfiring. It ran perfectly the day before, and only sat for about 10 hours between startups. I decided to change my fuel filters (Motorcraft replacement) and I took it for a test drive. It seems to smooth out when not idling, but as soon as it goes into overdrive it feel like I’m driving on rumble strips. If I hit tow/haul, the severe vibration goes away completely. 

I’m at a loss because the vibration when going into overdrive signals the transmission, but it shaking at idle doesn’t. Any help would be appreciated. 

Also, there is no check engine light