It was raining today, not that the weather conditions should effect this.
On my way home from work today. It was working great til the on ramp of the freeway. No crazy acceleration or anything. The speedo needle dropped to 0 (not below). About half way through the drive, it started going crazy again. After the freeway (about 3/4 of the way) it dropped back to 0 and stayed there.
I will let it sit until tonight and see if it works or is at 0 again.