Better to get a High output alternator or a capacitor?

my setup seems to be killing my alternator cause the lights dim and at a stop my battery gauge gets real close to the Low. Should i get a High output alternator or a capacitor? My truck is a 07 ram 1500, my amp is a Alpine - 500W(rms) Class D Mono MOSFET Amplifier with Adjustable Crossover, and my sub is a (400-rms) 12'' Kicker CVR bridged at 1 OHM. the settings on the amp are (gain-75%  Bass EQ- 12db LPF-75Hz)

Any answers and opinions will help, thanks
moby dick and mighty mightor - cartoon resource website entry  149