Speedometer Problem

Im not sure exactly where to put this but here goes.  My speedometer is wavering around when I'm driving a constant speed.  As I shift through the gears it bobs up and down sort of with the tack.  It's way off and showes about 40 when I'm running 60.  It will waver about +/- 15 mph while driving.  Any ideas what could be my problem?  It randomly started doing it while on a trip.  

What jeep do you have? Its more than likely the speedometer sending unit.  
Get a real jeep! (pre '75)

Could be the sending unit, the wiring connectors, the wiring, or the drive gear in the x-case tailshaft housing could be stripped.

Did you replace your tranmission and head? Did you remvove the speed sensor from the x-case tailshaft housing when you replaced the tranny?

The speed sensor is indexed in the housing according to the number of teeth on the drive gear. Did you index the sensor correctly?  

Ive got a 2000 Wrangler Sahara. I put on a sye kit a while back.  There was a new sensor to put on if I remember correctly, but there was only one way to put it in.  It had read right for a while except for the difference in speed from 33's which I expected.  I just unplugged the sensor when I rebuilt the tranny.  I've not had much time to look at it but I will check out a few of those things.  

Which SYE did you install?

If it's one of the Super Short varieties, like JB Conversion's or Tera Flex, then there would not be a drve gear, only a tone ring.  

It is a super short kit I believe from Rugged Ridge, and your right about the tone ring.  I pulled it off and it looks ok but the sensor may be bad.  Is there a way to test the sensor at all?  

I finally figured out my speedometer problem.  After talking to the guy I bought it from, he suggested I make sure the nut on the output shaft yoke was tight since that is what tightens the tone ring the speed is read from.  It wiggled when I pushed on it, YIKES!  Retorqued it and it works like a charm.  Thanks for your suggestions guys.