Parfive00

Replaced the alternator due to low voltage. Now it will not charge at Idle. Under driving conditions it will run at 13.8-14.3 volts but at idle and under heavy load (seat heater, rear def, bright lights) the voltage drops till the car dies. Battery tested ok and even swapped the battery with a brand new one and same problem. Back to back ALT replaced and same.issues? Looking for answers!

80es300

Where did you get the alternator? It is not uncommon for auto shops to have bad alternators. You can ask them to do bench test of the alternator.