I'm with Jerry on this, sounds like a sulfated battery.
How many other accessories are you running? I've got a Mallory ignition w/Promaster coil & a 3RLi spark box, electric fan, fog lamps, H-4 hi output headlamps, DeLuxe heater, and about 450 watts of stereo, all runing on a 65 amp alterator. I don't think I've ever seen the amp gauge (afteramrket Autometer, no the original) go any futher that 30 amps with a full load on it. Unless you're running an extremely high power stereo or a snowplow, I don't really think you would need much more than 60-65 amps.
