2005 GMC Sierra Speedo Problem

My speedometer on my truck is malfunctioning majorly. It doesnt go below 60mph when I am stopped and pegs out at 130 when I am only going 40mph. Being there are no codes or warning lights coming on, I am thinking it is a bad Speed Sensor. Also, I replaced my original Cluster, which was doing the same thing, a year ago with a rebuilt one. If it is a Speed Sensor, is it fairly easy to replace myself? I can generally diy things if they are fairly straight forward. Thanks.