Your truck is hainted (southern derivative of haunted, but somehow way worse).
Shove it into a ditch and forget about it.
You may want to first try just trowing the speedometer as far as you can and replace it with a new one. If you do that, drive cautiously in case it doesn't result in exorcism of the haint.
I have bought aftermarket speedometers and they work just like the originals (somewhat inaccurately).
The only difference that I can see is that the bezel of the reproduction ones are rounded in cross section. The originals are bevelled in cross section. Very minor and hardly noticeable.
