This is a long shot, but I just pulled apart the top end of my motor, and since I've boosted the car (and this running issue slowly started happening) I realized my VANOS seal is DONE for! Parts on order, not sure if this could be the cause, but the known symptoms sure point in that direction, and other than that everything on the motor looks fine. Maybe someone from Miller could comment if that could cause these issues? I'll reply once the parts come in.