Did you have problems before you replaced the cable? (i.e., why did you replace the cable to start with?) Assuming you've got the correct speedo gear, it could read slow because the indicator spring anchor has slipped, but that would be highly unusual for it to slip in the tension direction. The stop is a tang built into the speedometer head. It can be adjusted by bending the tab, but it is unlikely that this spontaneously changed either. I've seen many speedometers that start out slightly below "0" If your speedometer just started acting crazy when you put in another cable, I'd make sure it is plugged into the back of the head properly, make sure the threads are engaged properly at the trans, make sure that the adapter at the trans is turned to the proper rotation for the tooth count of the gear, and if all that is OK, I'd pull the cable from the housing and inspect it very carefully along it's length.
Good Luck,
"Dennis W"
