I Hope someone can help.

I have a 1991 Ford F150 351 E40D tranny 4wd with 123,000 miles.

I live in Alaska, when it gets cold and the truck sits overnight the speedometer reads 20-30 mph faster when I first drive it until it warms up, about 20 minutes.

I don't have ANY problems if the temp. is above about 25 degrees F.

The speedometer isn't jumpy, it just reads too high for awhile, any suggestions.

Thanks,
John