Could the problem be the pump itself? Is it slow to accelerate on the ground too or only in flight? If yes, I would think you could watch your PW value as you move the stick to full power, if the voltage to the pump is increasing appropriately then the problem is either your pump or a clogged line/filter or something inside the turbine. You might also want to check your throttle curve settings in both the Fadec and your transmitter.