UNUSUAL ALTERNATOR CHARGE

I HAVE A 1982 MAZDA RX-7.385,500 MILES. THE ALTERNATOR HAS ALWAYS SEEMED TO BE A PROBLEM BUT WORSE AT TIMES. VOLTAGE REGULATOR SEEMS FINE. NOW HERE IS THE WEIRD THING.I WILL TRY TO DESCRIBE IT THE BEST I CAN. STEADY SPEED LETS SAY 2500 RPMS. VOLTAGE "FLICKERS" FROM 14 DOWN TO 13. AND AT NIGHT IT CAN BE SEEN IN THE HEAD LIGHTS. NOW WHEN I HIT THE GAS THE VOLTAGE DROPS DOWN AND STAYS THERE, BUT IF I LET UP ON IT IT WILL RETURN TO 14. NO MATTER WHAT RPMS THE PROBLEM STILL EXISTS. ALL TERMINALS AND CONTACTS CLEANED. THIS IS ONE OF THE FEW PROBLEMS THAT HAS LEFT ME RUNNING INTO DEAD ENDS. WHAT ON THAT CAR COULD CAUSE THAT KIND OF POWER DRAIN OR WHATEVER.(AND ALSO IT DOESNT MATTER WHAT KIND OF LOAD IS ON THE ALTERNATOR)THANK YOU