Hey guys, I hopr someone can help me with this. She's a 99 F-250 V-10 Super 4x4 with 221,000 miles. Runs great and has given me no real engine or mech problems. 2 or 3 weeks ago I noticed a change. As I come slow to a stop, at 15 or 10 mph I get a vibration that feels like I'm driving over a fodder strip, or shoulder groves, or something to that affect. It feels almost like driving on tank tracks. Also, when I driving down the road (35 mph or 65 mph, it doesn't matter) as soon as I take my foot off the gas, the engine revs higher and it feels like I'm being held from behing, just like what an engine brake would sound and feel like. Any ideas??

 

Sounds like your in overdrive to me. I'm not to learned in the Ford Trucks but maybe your overdrive button(?) is stuck

 

I thought that too at first but when I push the overdrive button the tranny downshifts, so I didn't think that could be it.

 

I'm starting to think there's something in the rear-end needs fixing. The tranny seems solid.

 

Sounds like the transmission is slipping. That would be the rumblestrip vibration you are getting.
Have you gotten any warning lights?
Most of the time, if you run the codes you'll get P1870 with a problem like this.