Speedometer reads double actual speed

Well I don't' have the answer yet but Thanks for the ideas, I found another site where someone else had the same symptoms, and they replaced the head to fix it. I think I can borrow one but the truck is being used a lot right now. When I can I may try the whole panel as suggested earlier.
I also got some info from the local Pete shop, the value for the speed sensor is 270 ohm +or- 10. I checked a new one @ 263 and mine checks @ 283, 3 ohms out, but I cant' believe thats enough to cause the problems described. Note; this is for a 2 wire "old style" sensor,"1998 model".

 

Hi, I thought I would finish this for anyone interested.
The short story is I replaced the speedometer head with a used one and it seems to be OK now, we are so slow right now I have only put a little over a hundred miles on it but I believe it is fixed.
Thanks to all for your help.

 

LOOK UP!!!

 

Hey Gambi,
I found a used one and so far so good, Pete's price is just insane. For your info, if you haven't thrown the old one out, the used one I got appears to have been repaired somewhere. The case has been cut by the odometer, and there was a sticker over it that said something about the mileage on the speedo may not match the mileage of the truck. With the sticker removed, the odometer mechanism was in full view, now that you said that the odometer was your problem, makes me think it may be a more common problem, and may be repairable.