odometer fraud
 

is it true that if ur speedo is bouncing that it could because someones messed with the odometer?

That is normally due to binding or wear in the cable, cable connections or gears somewhere between the drive and the cluster/gauge in a mechanical speedo linkage. Early Dodge electronic gauges used a combination of a mechanical drive gear coupled to a signal generator (VSS) to drive the 1st Gen electronic speedos. This type of speedo setup may also be subject to the same symptom for the same reason, usually a bad drive gear.

I would bet its the cable or gear...if your talking about the 98 you have.

is there a way 2 tell or just replace both?

Like just about everything else, it helps to take it apart and have a look. Some things are obvious, most are not. JMO.