There are two speed sensors. one in the rear pumpkin and one in your tranny. I would change the one in the rear end first. I ended up finding a short in the wires about a foot from the rear end sensor. the sensors are known to go out though and will cause the speedo dance. Here is a link. The $11.99 one should worlk just fine. Pretty easy to change too. Just unplug, take out the one bolt and pop old one out push new one in. While we find your parts, please enter your ZIP Code at PartsAmerica.com What year is your truck? These parts were for my 2000.