Stock is a rod, aftermarket is a cable. Guessing you have an aftermarket kickdown cable? (or TV if AOD).
Trouble is this cable isn't generic cable. If you feel the cable it is smooth. The standard cable you will find isn't smooth, it's bumpy. That will eat away at a cable sheath over time.
With luck you can trim the outer sheath which will make the inner longer. If not, you need a whole new cable. If it is a good brand of aftermarket cable, and you ask nice, you might be able to get a new inner cable directly from the manufacturer. But that involves you going directly to the manufacturer.