I have a 2004 f350. The truck runs perfect for the first ten minutes or so on the highway. And then you can feel something very slight. I'm not sure what it is. But if you wern't waiting for it you would never feel it. Anyways right after you feel this the truck begins to shimmy badly in overdrive at around 80 km. If you kick it down a gear it is fine. The allignment is good and I have rotated tires in case I had a bad one. I've changed ujoints in driveline. Front end, including ball joints are all tight. What gets me is it is like it has too warm right up before it does it. I thought maybe an injector or something throwing the engine out of balance. But there is no ehaust. Everything seems normal. Maybe it is my imgination but the engine seems to be running rough when it is acting up. If I stop for an hour it is fine again. It starts up after I have been on the highway for awhile. Could it be an engine problem. Something shaking the engine so bad it causes a bad shimmy. Any help wpould be very much appreciated

 

Check/change transmission fluid?
If it only does it in OD, I would say it's somehting to do with either the tranny as a whole, the torque converter or the OD gear specifically.