Remove the VSS from the transmission. Should be the plug, attached to a rod with a gear on the end of it. Make sure the gear is not worn out. Also make sure that the rod is connected properly.
In another note. Jack up front of car, place two Jack stands under car, one on driver, one on passenger and keep the tires off the ground. Using the help of a friend, use a test light to make sure you have power at the VSS plug on harness side. Plug vss up and put into 1st gear ( or drive is auto) and allow the tires to roll. Speedo should read, if not, wiggle your wires at the plug. May have loose connection.
Lastly, replace your VSS relay. Should be located under hood in fuse box if I am not mistaken.