Speedometer/tach problems F350 6.0
Just bought a new 06/f350 6.0l. 500 hundred miles on it now and the tach and speedometer don't work sometimes. Coming to work tonight tachs on 500 rpm and speedo is on 95mph. I'm going around 70mph I figure. This is the second night it has happened.. Truck shutoff is now reading 15mph. I tried turning the truck off and re-starting it but it didn't change. It appears to drop back to 0 mph after stitting for a few hours then works correctly for a while until I stop a light then will be erratic after that. Same for the tach. I don't see any TSB listed for it. Any ideas?
It is also around 0 degrees here.