1980 Chevy Camaro Car shuts off, turns back on while drivin

Hello. I have a 1980 Camaro Z28 350 auto. I drive it about twice a week. Maybe 40 miles a week.

I'm going to be as detailed as possible. Sorry if it hurts your eyes!

About 5 months ago, it started shutting off and turning back on while driving. The headlights and electrical stuff stay on, but the engine shuts off. It seems to only do it after it has warmed up.

Five months ago I replaced the ignition coil ($20 cheapo from Autozone), cap and rotor (MSD). This fixed the problem. Until about a week ago.

I replaced the ignition module ($20 autozone), and its still doing it. My question is, what else could it be?

I found an entire hi-performance 65,000 volt Distributor that includes coil, upgraded module, pickup, cap, rotor, shaft, and gear on ebay (gr8hotrods) for only $53. In your opinion, would it make sense to purchase it?

I should also bring up that I have noticed sometimes at night the voltmeter reads significantly lower than usual, and the dash lights are slightly dim. Then all of a sudden it will jump back up to normal and the lights will get brighter. Could this be related? Could a bad ALTERNATOR be making it shut off?

Thanks for your input and your site. I'm a student on a budget, and I'm trying to do this stuff myself and spend the least amount of $$$ possible, so it really helps.

Thanks again,
Patrick