Well..over the last several weeks I have attempted to resolve my speedometer issues and so far so good.
As it stands now..in my situation..I do not believe the cable or the gear at the tranny were bad in any way. I drove the car without the instrument cluster to watch and feel the internal speedometer cable. All appeared to be correctly functional from what I observed.
I dissected the instrument cluster and removed the speedometer itself. The speedometer consisted of a weighted wheel attached to the needle and a "C" shaped bracket that orbits around the weighted wheel. The "C" shaped bracket rotates at the speed of the speedometer cable. At slow speeds the "C" bracket did not make contact with the weighted wheel. However, manually moving the needle (& weighted wheel) to another point higher up on the MPH scale caused slight contact. Therein, I believe, is what was causing my speedometer needle to hover at and around 120 MPH anytime I actually exceeded 40 MPH.
Basically, I spent a couple hours bending and twisting on the weighted wheel and "C" shaped bracket till both rotated freely and without contact in any form. The procedure was a major PIA, but still cheaper than buying another speedometer.
There is a slight chance that the calibration of the speedometer is now off. Presently, just running around town and in traffic..everything appears to be just fine. However, as soon as I get some free time and a chance to hit the open road with a stopwatch in hand..I'll make a better determination. Making that adjustment will be easy compared to the rest of this mess...