Yeah, it seems to me it could be the fact that it is drawing power from the laptop.
Do you have the laptop plugged into the power socket?
If so, have you checked its on? (My grandparents made this mistake, and wondered why the screen was darker and was running slower than usual)
I'm sure its just a simple problem like that anyway
If for example you didn't have the laptop connected to the power, this would be why it would be running slower if the docking station didn't have its own power.
Hope this helps