^^ It may not be a direct problem with the power steering but it sounds like something is bogging the motor causing the alternator to bog as well.
But back to the issue. Thought maybe your wheel bearings were goin out but you replaced the hubs and that wouldnt explain the dimming lights.
When does it happen most often? Driving straight lines our turning corners? And does it do it when you just turn your wheel all the way each direction while sitting still?