Where is the speed sensor on a 1993 Ford F250 extended cab 4x4 pickup located?

The speed sensor on a 1993 Ford F250 extended cab 4x4 is located in the differential housing of the rear axle. It's not on the transmission. It's a magnetic sensor that reads the speed of a reluctor ring attached to the differential.

To be precise, you'll find it on the passenger side of the rear differential. However, you'll need to get under the truck to locate it. It's usually a relatively small sensor with a single wire connector. It may be bolted directly to the differential housing or held in place with a bracket.