Hi Kyle,
This failure mode happens when a little bit of water enters the speedo mechanism and then freezes. , When the water freezes, it expands causing the brass ',bourdon tube', to expand, in turn causing the pointer to go upscale. , The only way to fix the speedometer is to change the bourdon tube inside of the gauge. , Please contact Wanda at the factory, 603-5753-6362 x201, and she can work with you on getting your speedo repaired/replaced.
Thanks,
Ken