1996 Pontiac Bonneville sudden electrical power loss

MY1996 BONNEVILLE WILL LOSE SOME ELECTRICAL POWER. THIS HAPPENS WHEN SLOWING DOWN FOR A STOP OR WHEN IDLING. THE CAR WILL SOMETIMES STALL WHEN THIS HAPPENS BUT ALWAYS STARTS IMMEDIATELY. I REPLACED THE ALTERNATOR THINKING THE PROBLEM WAS CAUSED BY THE VOLTAGE REGULATOR, BUT, THE PROBLEM STILL EXISTS. ANY ADVICE ON THIS PROBLEM IS GREATLY APPRECIATED.