Speedo issues

[srjd]

Got in the truck today let it idle for 10 min all is good. The second I put it in drive and hit the throttle my edge warning light goes off and says vehicle over speed. I look at the speedo and its maxed out. Stays there for a second and then shoots down to 10km/hour the speed I was taking off in. It was fine the rest of the day. Truck didn't skip a beat. In all honesty if my edge didn't go off I would not have knoticed. Any ideas