yea, i'm pretty sure it's a gear on the sending unit, thats bolted to your transmission, how ever i wouldn't know how you would go about calculating what new one to get lol.
nope 89-95 have what is called a "drac" module... dont remem what it stands for exactly...but its something to do with the rollout of the tire and the gear ratio of the rearend.
last time i ordered one for a guy it was around 125 $ if i remem right. and the place we send our clusters in to get fixed is who had to build it for us.... they are up under the drivers side of the dash tucked aways up in there.
but to answer your question no its not part of yours..... its only on tbi computer controled motors/trans 700r4-4l60e... not on carbed ones with a speedo cable/gear th350 or th400