2003 V8 -Starting yesterday morning noticed my speedometer was showing I was going 85 miles and hour on a surface street, when I stopped it showed I was going 100 mph. When I would take off it would go back to 85mph and to 100 mph when I stopped. After about 15 minutes of driving it started to work properly. This morning it showed 0 mph for about 3 minutes then went to 100 mph for about 3 minutes then moved to 85 mph when moving then to 100mph when stopped. It did not work properly again. The odometer, tachometer work correctly. Anybody have any ideas?

 

03's are electronic- its probably the speed sensor or the wiring- i'd start checking those first.