Speedo help please!

[Buzzman]

Hey There,
My speedometer continues its quest to drive me insane with its clicking and bouncing around. When I originally got the truck, it was hooked up for cruise with the two cables. Speedo didn't work. So I went with the single cable setup (lubed properly with liquid graphite - it's not the cable). It worked fine for a while, but when the weather turned cold, the clicks began. Tried greasing up the dash end, but that didn't help. So I picked up a used speedo on ebay, hooked it up to the cable without intalling it and it worked fine, but when I actually put it in the dash, the clicking started again. So it's not the cable, and I don't think it's the driven gear in the tranny. That leaves something in the dash - maybe the retainer clip is messing it up? Has anyone encountered a similar problem? Thanks!