Check/monitor BATTERY VOLTAGE AT THE BATTERY with a DVOM (digital volts/Ohms meter) while the engine is running.
Record battery voltage WHEN (or if) the engine shuts down. Very important to know if the voltage has exceeded 14.6 VDC.
You also should visually inspect the VOLTAGE REGULATORS for signs of melting, burnt spots, etc. Check for melted/burnt/browned/blackened bullet connectors (especially the ones on the RED or YELLOW wires). If any of these are noted- replace BOTH regulators, and any damaged bullet connectors.