lights flicker at cruising rpms fine at idle?

Usually flickering or pulsating lights are caused by a diode on the rectifier plate being bad another thing that makes the lights flicker is a brush bouncng in the brush holder. We have a saying around the shop... "Just because it's new doesn't mean it's good!" a third thing to do this is a short in the secondary windings of the stator. I would take the alt back and have it replaced and go from there