Since various people have mentioned higher nicotine, keep this in mind: if you try to vape 6 mg nic liquid the same way you are vaping the 3mg liquid, you will probably want to lower wattage/voltage settings and maybe close the airflow on tank a little, giving you a little less vapor. You would be able to get too much nic pretty quick at 6mg on your setup. Some like more nicotine and 6mg is not completely inappropriate for your tank, but you would notice a difference.