I find that lowering the adjustable poles in a humbucker flush with the top of the pickup and moving the pickup about 1/16th inch from the strings helps get maximum output with stock pickups. You can use a shorter adjustable polepiece if it extends out the bottom of the pickup. Using a shorter pole will help conduct more magnetic field to the string with less loss of the magnetic field out the bottom of the pickup. Raising the pickup as close as possible to avoid the string from hitting the pole is one easy way to get more output from a stock pickup. Make sure the pickup has proper polarity and properly magnetized. Make sure all the volume and tone controls are in good operating condition and clean. Reduce the amount of excess wire from the harness, cavity, pickups and jack.