I got this from Tower Hobbies about the 3152 servo. You may be encountering what they describe:

S3152 Digital Servo Precautions,
-It is best to avoid long leads and Y-harnesses especially with
standard grade wires. If problems are encountered, consider using
heavy duty wire such as Futaba's Heavy Duty Series or Hobbico's
Pro Series, minimizing lead lengths, and/or removing Y-harnesses.
-Current Drain: Futaba S3152 Servo is Specially Designed for High-
Torque and High-Speed, Therefore Very High Current Drain Is Normal
At Startup. For Ultimate Performance When Using This Servo
Please Review The Following Points.
(1) When Using Systems With the Battery Fail Safe Function it Has
a Higher Cut-Off Voltage Setting Which Will Cause Shorter
Operation Time.
(2) When Installing the Servo Please Check Pushrod Linkage To Make
Sure There Is No Binding in Order To Prevent Excessive Power
Consumption and Decrease the Life of the Motor and Battery.