Is it imperative that a drb III scan tool be used for this?  I'd there another way this can be tested?  I've been looking at the power probe hook and a obd scan tool as an alternative?  Thoughts?

Well DRBIII tool would be the best.

 

OBDII might help out a bunch and see what the speed signal is reporting on the CCD network. 

 

Other than that I would say check the speed sensor circuit to the rear by disconnecting at the rear speed sensor and the ABS module. Using a paperclip make a jumper between contacts on the rear sensor plug. Now measure the ohms at the ABS plug and see what you get. This will verify the wiring for you. 

 

If you got time and can get the speed sensor out of the rear diff. Look and see if the tone ring is lined up to the hole. I've heard of one member that lost a carrier bearing the entire carrier shifted towards one side and the tone wheel was not visible in the speed sensor hole.

Thank you, Good information.  I've replaced the rear speed sensor and will perform the checks mentioned.  Question, Is the rear speed sensor the only speed sensor?  This is a 5 speed so I don't think one is up by the transmission but may be wrong.