I have a 95' T100 with about 160,000 miles. A couple weeks back the speedometer was not reading correctly. By the end of the day it wasn't moving at all. Since then it has worked sporadically. Usually moving between 5 and 20mph, occasionally higher than that and several times reading true for a complete 10 (or so) mile trip. I'm not sure if there is a typical cable with a gear in the tranny but I couldn't find any useful info or diagrams in my aftermarket manual (Chilton's?). Any advice/input on what might be the most common trouble spots would be greatly appreciated. Thanks.

The T-100 uses a std speedo cable from the trans. $75 if you need one from Toyota. The instrument cluster side uses an electronic pick-up at the back of the speedo. The speedo is electric. $250 for the whole cluster from Toyota.
I changed my cable (cheaper) and reduced my jumping of the needle. The new cluster would fix the rest but too pricey for me right now.

Thanks for the info. That will at least put me in the right direction. Pete