Semantics. It is a 4 speed and 4th. is o/d but it is basically a 3 speed and 4th.is overdrive. No difference than a 5 or 6 speed. A 5 speed is "usually" a 4 speed and 5th is a o/d and a 6 speed is "usually" a 4 speed and 4th. and 5th. are overdrives depending on who makes it and how the ratios are set up.
