I'm pretty sure Eddie is right here...it's the rotor more-so then the pads. With my original 4Runner calipers, I used- Hawk HPS, Hawk Superduty, and OEM pads. After about 3,000 to 4,000 miles of NYC heavy stop and go, my rotors would warp, end of story.
I switched to the Tundra S13WE (199mm) calipers and Tundra rotors two winters ago. I have had zero problems since, towing or heavy traffic.