I realized after asking the question that I didn't give enough symptoms.
Obviously I see it more at night (s10 lights are always on) dash lights, headlight flicker randomly. Very fast, time span between off/on is irregular, maybe 10 seconds, mayb 60 seconds. Smooth road, Highway speeds, I do not notice it at regular street speeds.
It seems to be speed related, does not flicker below 65mph.
I've had it to Chevy, they checked system and found nothing wrong.
Independent mechanic could not reproduce. But my wife sees it also. It's worrisom as I'm afraid they would quit altogether at night on highway.
That service bulletin refers to the problem and on newsgroup a person said he had it with his Venture and the mechanic fixed the problem after seeing the bulletin.
Wife and I take frequent driving vacations. please find the answer