New alternator, flickering lights

[StatutoryAPE]

what you were experiencing is called diode ripple...an alternating current leak through the diodes...with a description of your concern the alternator should have been exchanged the first time you brought it in...

the diodes change alternating current to direct current to operate your vehicle...a failing diode will leak a "ripple" on the dc current and can screw up a lot of things...many transmission concerns are alternator related due to the electronic controls...

Would this also cause idle rpm to fluctuate abnormally?