When you have the issue does your voltmeter droop somewhat at idle and or does the water temp start climbing compared to what your used to seeing?
If your sure of the Alt and water pump health you may consider going to a 6 rib (serpentine style belt) or a Gilmer cog type. Some folks are fond of the blower whine assoc with the Gilmer.
Mine uses the 6 rib and a March pulley bracket setup that moves the Alt higher even with the valve cover.
https://speedmaster79.com/pce4151004...mer-drive-kit/
Serpentine Pulleys - Pulleys - Ford Small Block 289, 302, 351 Windsor - Ford - March Performance
