Dog on it, I was slow in responding again. I was going to make the suggestion that the motor was not getting the full voltage. This actually could happen, just like the dim headlights on most of your cars. But if yours is working well, then it is getting full voltage. If there is 14 volts on the battery, there could be 11 volts at the wiper motor, which would cause it to run slow. I have not heard of this ever being a problem, but it could happen.
In my car the voltage to the headlights was 11 volts when the battery was 14. So I added the headlight relay. My horn would not work because it was not getting enough voltage, so I added a horn relay. The wiper will be next?
Congrats on yours, now move on to the other 6,234 problems.