The tremac trans is a 3650F brand new direct bolt on for a 2000 mustang. The speed sensor with the gear is from the old trans and matched to fit in new trans so the plug snaped in correct. ???
The thread does not state if the speedometer is off or not working at all.
Transmissions from 2004+ model year uses a different number of OSS reluctor wheel teeth. If the speedometer is off, this could be the problem. The number of OSS teeth can be corrected with a custom tune. It's the same issue as changing the rear-end gears.
If the speedometer doesn't work at all, then we need to know what the PCM "thinks" the car's speed is. If the PCM speed is zero, then focus on the OSS sensor. If the PCM has the correct speed, focus on the cluster.
FWIIW, the VSS sensor uses a gear. The OSS sensor does NOT use a gear. The OSS is a non-contact sensor like the ABS sensor.
Check out the following on more information regarding the differences between the OSS and VSS sensor.