Likely it has an aftermarket sending unit as your description fits. They are all crap.
Speedo, you saying if you spin the cable it works but in when connected to the transmission it does not? The speedo gear in the transmission may be installed incorrectly. In the FSM you will see the housing that hold the gear can be installed in 4 positions and depending on the number of teeth on the gear (set by rear axle ratio) the housing is rotated to a particular place. If wrong the gear can be pulled away from the drive gear and they don't mesh.