My 250 4.9L I6 runs rough until I get it above 55, especially between 3 and 4 gear, kind of hoppy and jerky can anyone suggest something to try to fix it?

 

So no one has any idea's? Am I missing some information?

 

Are you certain it's engine related? Generally, rough running has to do with RPM, not vehicle speed. If it's vehicle speed related, it could be bad motor mounts, tranny mounts, problems with the driveshaft, etc.

 

When was the last time it was given a complete tune-up? Typically low speed miss can also be caused by weak coil/ignition module, tired/mis-adjusted ignition points (don't know if the 83 had those), hairline crack in the distributor cap, worn ignition rotor, tired spark plugs/wires, EGR valve dirty or actuator tired....