Failed speedometer when it's cold outside

Why does my 2003 Chevy Trailblazer speedometer stop working when it’s really cold outside? Will this be expensive to repair and what does it involve?

I have the same problem. Usually after about 1 1/2 hours of driving between 60-70 mph it will begin to drop back to zero. If I stop the vehicle for 5 or 10 mimutes it will repond for another 1 1/2 hours. ??? help!