Thanks, Vano. I'll checked that site but only saw an option for 2wd models. When the big tires went on I upgraded to slotted rotors and Hawk pads, but as you said, that doesn't take the place of having proper sized calipers.
To be fair, the stock calipers have done a fine job so far but typically if I tow I'm using my own trailer which has brakes.. I've never really put it to the test with a full non-brake-assisted load going down the mountain but given the piston cracks I had when I last changed out the rears I'm not eager to push it.