Speedo Driven Gear Not Spinning

[Duts87ss]

I've got a freshly rebuilt 200-4R in my Monte that doesn't seem to be spinning the speed sensor (running electric speedo). No movement from the speedometer needle while driving and no speed reading to the ECM. If I remove the sensor from the transmission and spin it with a drill, I get needle movement on the speedometer. I've also replaced the driven gear and "bullet" with ones from a known-working transmission and get the same results.
Shifts seem to be just fine, any ideas what the problem could be?

 

[MeanBuicks]

Well you've verified everything back to the drive gear which is on the governor. Pull the pan and the governor cover to see what's happening with the drive gear. If the transmission shifts fine then the governor is spinning & functioning but perhaps the portion of the governor gear that drives the speedo driven gear is damaged.

 

[SSedan64]

Small gear on Gov/Drive gear is driven by Output Shaft.
Large gear on Gov/Drive gear drives Driven gear.