Check the pigtail... We've seen them go out a lot. The wire pulls apart from inside the insulation. That, and the speed buffer. It's a little white box behind the glove box. The VSS wires to that box. Then sends the signal to the cruise, ECM, and dash. Make sure u have 12 volts goin to that buffer. The buffer goes out a lot also. If it won't shift, the problem will lie between the sensor to the buffer, or buffer to the ECM. Need any info let me know I can email you the diagram. If you have an ohm meter, tracking the problem won't take long.