speedometer reads 20mph when engine is off
 

I have an 04 LB7 with Edge w/attitude tuner. My speedometer all of a sudden starts indicating I am doing 100 mph on the interstate and cars are passing me. My GPS says I was doing 75. When I stopped the speedometer indicated 20 mph. It appears to be through the range of motion on the speedometer...about 20-25 mph too high. Any ideas?

Speed sensor on the tranny or rear end

I finally got time to change out the speed sensor and it did not help. The speedometer is now pegged out(happened before I changed the speed sensor) and has not moved. I have researched what limited stuff is out there and all indicators say my instrument cluster (panel) is faulty. Any ideas to whether this is right or wrong?

the gauge cluster is going out on you. there used to be a warrenty on it, idk if its still going on. but it happens to alot of the 03-04 models.

Thanks for the followup. I will check with a local dealer in regards to the warranty. If it is not covered any suppliers you might recommend? Again thanks for the inputs.

yes it should be your cluster ... happend on my 04 tahoe ... i was told it was past the warranty and was like 400-500 to replace ... so i just got used to reseting my avg speed on the tripometer when it first resets it gives your current speed ... also got pretty used to speed to rpm relation so could tell what speeds (relatively) i was doing and on freeway to be safe it would check then set cc so not to worry