So I have a 92 F350 159000 miles on it. The truck runs and drives great except not that long ago my overdrive light started flashing, and the rpms will jump. For example when I'm driving at 55mph it's at 1500 rpm it will jump up to 2000 and back down and repeat. The truck has shifted kind of hard the whole time I've had it. Anyone with any insite on this? Thanks.

 

My insight would be to read the codes. That will tell you where to start. Without the codes all I can tell you is that something is wrong.