[Chumley60]

Wow. I found a reply to this old thread in an old mail box. Surprised any of it still works.
It may be the speed sensor, but what I ultimately did to fix my problem was get the instrument cluster out of a wrecked Nissan suv at a junk yard. It cost $60 but the guy gave me a 30 day warranty to make sure it was good. It was, but I still had the bad speed reading due to the oversize tires. Turns out there is a small trim pot on the circuit board in the back of the instrument cluster. I had to remove the cluster to turn it with a little teeny screwdriver, but it did adjust for my 31" tires. The control is not labeled, nor are there any marks. I used a gps and just winged it with trial and error. Works fine now.
As to the squealing mentioned elsewhere, it went away for a year or so, then started back just recently. I had the whole front end torn down, and the mechanic could find no problems at all. It just seems to come and go.