The top two terminals, which you marked 1 and 2, are the slow and fast speed terminals (or the fast and slow - the fsm isn't real clear). Anyway, doesn't matter; there should be very close to battery voltage coming from one or the other depending on whether the wiper switch is on high or low. There isn't less voltage for low - it's the full volts. The ground side is not one of the wires in the connector but instead the body of the wiper motor is supposed to provide the ground. That's a possible source of corrosion and poor electrical connection.
It's strange that you are only getting 11.4 volts when you tested terminal to ground: what was the ground you were using? From the wiring diagram in the fsm, I can't see why you wouldn't be getting very close to battery voltage on that terminal. Unless the wiper switch has a resistor in the circuit, which seems very unlikely.
You could try a jumper cable between the neg bat post and the body of the wiper motor and see if your wipers speed up. If they do, you'll need to clean the bolts or rig a stout ground wire to the wiper motor body.
I don't know how easy it would be to detach the linkage from the wiper motor arm, but if you can do that, you'll be able to see how much resistance there is in the linkage. Make the disconnection at the end of the motor arm, not at the motor shaft, if possible. (I haven't worked on mine so I don't know how it attaches.) You want to avoid disconnecting at the motor shaft because basically you don't want to pull any splines apart (if it has any) without first making a clear match mark: wiper motor park positions are usually VERY fussy and particular. In fact if you get the position messed up, usually it's a real bitch to get it back into the right position.
If you don't have an fsm, google 1993 toyota pickup service manual and check the section BODY ELECTRICAL - WIPER AND WASHER SYSTEM for more details and troubleshooting help.
Good luck! As the owner of a 20 year old toyota wiper motor, I'll be very curious to learn what you find...