Alternator Problems!!!

[mongo93]

I've got a 93' LX 5.0 that is heavily modified and the 75 amp. alternator is not doing the job any more. The lights dim when the throttle isn't pushed in,like at a stop light or waiting to pull out into traffic, my question is what amp. alternator should eleminate this problem? I thought of installing a 100 amp. alt., but I'm not sure if that will be enough. Should I go with a higher amp. alternator than 100 amps? The only thing I've changed eletrically,besides whats under the hood,is the stereo. Changed out the factory radio with a Pioneer cd player. Could this be the reason the alt. isn't charging like it should? Any suggestions to solving this problem would be most helpful. Thanks!