My recently acquired conversion van with 38,000 miles has a sticky speedometer. Sometimes high, sometimes low and sticks momentarily on the way up and down. Is it a bad gauge or is there a sending unit on the transmission that controls this?

 

Plug in a diagnostic scanner and go for a drive.
If the speed on the tool is normal, then the problem is your cluster. If it's not then it's the sensor.

 

Probably the stepper motor in the speedometer. They can be replaced instead of replacing the cluster and they are not very expensive..

 

Thank you. Any idea as to source of supply and can it be a do it yourself job?

 

I did a 2003 Trailblazer and it was easy if you can solder. I replaced all 6 while I was in there. The 1999 is a different stepper motor and I am not sure how easy it is. They are available on Ebay and you can look to see if Youtube has
a video on how to do it.