S14 Speedometer Malfunction?

[s14SRguy]

incorrect/faulty speed sensor.
changing wheel/tire size shouldn't make that much of a difference.

Odds are your s13 trans still has the s13 speed sensor.
Make sure you get the s14 speed sensor, as an s13 won't match up properly with your cluster.

s13 and s14 speed sensors are the same size, bolt in the same, they just send different electrical signals. Odds are when the previous owner did the swap they didn't replace that sensor. If there is no difference after replacing the speed sensor then your cluster might be going out.