Was driving down the highway when my speedo slowly started to decrease in speed until it held at about 35mph even though I was going over 60mph. It started making a grinding noise coming from the dash. But when I slow down to anything under 20mph, then start to get going again, the speedo works fine until I hit about 45mph then it will start grinding again then drop to about 25mph. It also killed my cruise control.

anyone know whats causing that? thanks guys.

 

Since it resolves itself when you go under 20, then returns and makes noises, the gauge is probably physically broken. Otherwise I would say check the VSS voltage while spinning it by hand (it should pulse 5V), or check wire for a short to back of IM.