Have you tried the usual methods such as: turn up neck pickup, turn down bridge pickup, turn down tone control, vary right- and left-hand technique, pluck closer to the neck, use lighter gage strings, boost bass control on amp, turn up volume on amp, experiment with cabinet placement, etc?
Anyways if you want to throw some money at the problem, there is a great comparison of replacement pickups here:
"J" pickups discussion and comparisons.