Speedo Help

[87GMCChris]

Ever since i bought the truck, the speedo has been out a bit. I got used to it, but today i had to fix my exaust (one of the nuts backed off). While i was under there i pulled the speedo assembly(?) apart. Its weird and have never seen this set up before. ok... Speedo cable from dash >> then to an adapter, that has 1:1 stamped on it >> then to the trans. The gear is in perfect shape(thought it may have had a couple teeth missing or striped). Although there is a rod jammed in there that takes the adapter(with kinda keyway thing) to the plastic gear(square)... well it was bent, so straightened it and put it back in. had someone go ahead of me at the speed limit and same reading.
My question being, could the gears in side that 1:1 adapted be striped or something? Or could it be at the speedo gage? I don't think its at the gage because if i drive near a curb at a slower speed, say 20(Km/h). I can hear a ticking. And sometimes with the windows up, i can sorta hear it resinating up through the dash. Any comments and advice, or if this has happened to you, let me know please...

PS: Km/h R=Real speed and G= Gage.

50R = 40G
60R = 50G ish
70R = 55G ish
80R = 60G ish
90R = 80G ish
100R = Unkown yet. And beyond this i am unsure, due to the fact i don't travel past 100km/h >> 60Mph