'02 speedometer craziness

["John R. McWilliams, DC" <mcwilliamsdc@xxxxxxxxxxxxx>]

This week the speedometer of my '76 2002 has become even more "optimistic"
than usual.  Good until ~ 40 mph, but then it shoots up to indicate 80-90 mph,
with a steady slight oscillation, even if I'm only traveling at 45-60 mph.
When slowing/stopping, it will continue to indicate a high speed, then, when
my actual speed is 15-25, it will drop quickly from 80-90 to zero as I stop.
I've used dry lubricant on the cable in the past; never lubricated the back of
the speedo unit itself.
Any suggestions?

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