3mm isn't that low, even 2mm is still decent live left. According to this page
at the Acadia forum, new OEM pads are .37" thick, or a bit over 9mm. So at 3mm, you've got 33% of the pad life left, 2mm is a little over 20%.
Look at it this way, at 3mm left you can go half as many miles as you've got on the car before metal on metal. So if you're at 50K, you won't ear through the pads until 75K. 2mm left means you can go 28% more miles, or 14K if yo're at 50K now.
Personally, I don't change mine until I'm down close to or at 1mm thick.
Heh, just noticed this post is 4 months old. Oh well, good info that might help someone anyway.