Have you connected the 3 phase wires from the motor to the controller while testriding? Without power to the controller, this might damage the controller... (When the wheel are turning, power are generated, and can in some (rare?) cases blow the mosfets in the controller when no battery are connected.)
Try disconnecting those 3 fat phase wires from the controller and see if the resistance eases up.
I guess that it's possible to tighten the spokes so hard that you disfigure the hub, but that would be rare.... Besides, that would produce a mechanical gnashing noise from the hub...
Edit:
Also, if those cables are not connected, make sure none of them are shorted to each other; that would create a significant resistance.