Flareboyant
I've repaired two gm cars that did this-It indeed was the regulater. While in there, why not put a diode trio in there also. When they go out - (usually just one one the group) you'll get a faint glow of the alt light but still charge. Also never run your car at the exact moment another car is being started when jumping someone off. This imposes a load that the alt. is not designed to take. Good Luck