contrail1

Hey guys help me out, I have a 94 Mustang GT and my voltage gauge on the dash moves back and forth; when I hit the gas it rises and on idle the voltage is returns lower than normal.Should I replace the voltage regulator or the Alternator, by the way I have a200 amp alternator right now.In case its the regulator is there a certain type of regulator for the high amp alternators? Or do I need another alternator? By the way the alternator is only 2 years old.