Speedometer suddenly reads 40mph at rest, and goes up from there quite accurately. 2004 model, with only 39000 miles. Any ideas to correct this?

 

might just be debris in the IP, might try removing it and blowing it out with a can of air duster....

 

There is a recall on GM dash clusters. I had the same problem with my 2004 Trailblazer and my 2005 Silverado 2500HD...visit or call your dealership. You must provide your VIN and they should take care of the issue FREE.

I believe the only condition when they won't replace it is if the vehicle has over 70,000 miles.

hope this helps.

 

7 years and 4 months, 39,900 miles. Seems GMC is prepared to supply parts, and I pay for labor. $170-00.