(A/C, lights, window defogger, and every possible load) alternator top 30 amps, and voltage drops down (alternator sends what car demands, or less if damaged). If so, yes you have an alternator issue, and I would not blame the regulator straight. Are you looking to repair alternator, or will buy a replacement?
My car ETK have part numbers for 90A, 115A, and 140A. Do you have big power sucking audio system, heavy use of High beams? If so, I would go at least for 115A.
If you would attempt a repair, check stator, diode assembly, and brushes first, then rotor and finally regulator.
Now I would like to understand why the GM is working fine with low battery, or was it low before and now is OK?
Javier