A) Double check that the wastegate arm is attached to the wastegate actuator.
B) Make sure your wastegate isn't doing what is pictured here. The red dimension marks where the bushing that the wastegate arm passes through started to come out of its hole. That offset should not be there. I had SUPER lag when this turbo was on the car. Notice that even though the wastegate is closed, there is still a large gap between the flapper and the wastegate hole. http://img263.imageshack.us/img263/3998/failgateillustrated.jpg