irratic speedo
 

I recently went out and started my 03 dodge desiel and when it started the speedo was jumpin around from 20 to 100mph while idling. So went ahead and tried to go and when i moved it the truck shook and died. Its tryin to take off in overdrive so it kills engine when it moves. Anyone had this problem or know how to fix. Help!!!!

Mechanic has now had truck almost 3 wks and still cannot find problem. Please help!!!!!!