Charging system issue

[Knucklehed7]

Im having a charging system isssue. My truck is a 1985 chevy c10, base model. No power accessories, except lights, radio, aftermarket fan, gauges, and windshield wipers. My alternator when tested with a voltmeter is only putting out 12.2 volts. When I apply throttle the voltage starts to drop off. Brand new battery, brand new alternator, new v-belt, new starter, new positive and negative battery cables. I need some helpful ideas of why I'm not getting the proper voltage. I know its supposed to be upwards of 13.4 or more. Any help would be greatly appreciated. Thank you for the help.
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