I own a 1998 ford taurus. I am experiencing a problem with my vehicle when the speedometor is not working the car will not shift gears. But when the speedometer is working the car shifts fine. I recently changed the speed sensor and still have the same problem.

Yes. The speedometer (i.e. Vehicle Speed Sensor) provides important input information to the Powertrain Control Module (PCM), which controls the engine and transaxle. If there's a problem with the VSS, it affects Shift Solenoids 1, 2, and 3 in the transaxle.