95 F350 Speedo problem

[OLD DAWG]

I have a 95 F350 4x4 crew cab tow vehicle that is having speedo problems and I'm looking for suggestions/answers. It has a 460 with an auto tranny and at speeds up to 8-10mph the speedo needle won't work, then it will kind of jump or bounce up to the indicated speed and will be fine at higher speeds. I've been told that it has an electric speedo so I guess that leaves the cable out. I've looked on the tranny and on the transfer case tail shaft for some type of sensor but can't find one. Any suggestions? :(
Thanks in advance, OLD DAWG

[rabidranger]

There is a VSS sensor in the top of the rear axle that reads off a tone ring in the diff. Check the connections at the sensor.

[demonranger]

First suspect is the VSS as rabidranger pointed out if the connection looks good then I'd replace it as they aren't very expensive about 25 @ autozone they list a page for the parts house to look up for a test procedure.

[OLD DAWG]

Thanks guys I'll take a look this weekend. OLD DAWG