/6 runs great, randomly stumbles and dies...???

After it dies pull the air cleaner and look down the carb throat with the engine off. Give the linkage a pull (open the throttle) and watch to see how much fuel squirts into the carb. It sounds like you are running out of fuel to me.

It is very possible that the filter sock in the fuel tank is clogged or that something is floating around in the tank and randomly plugging it up causing your car to starve for fuel.

I heard a story a few years back about a fwd small suv with an intermittant low oil pressure problem. After the engine was replaced the factory tore it down and found a pay stub of one of their engine plant employees floating inside the oil pan. It would occassionally block the pickup tube I imagine he got fired, but the same principle applies to rust, leaves, and random debris. I would flush the tank and install a new filter.