I have a 2004 6.0 F250 and I'm trying to figure out when I'm driving at around 50mph, I feel a slightly shake on the truck. Now after driving it more and more it doesn't do it again. Anyone knows what this is or had a issue with this?
Thank You

 

Is the converter locked up when it starts? Can you press the accelerator to kick it out of overdrive and the vibration stay or go away?