60-70mph wheel shake/vibration is almost always a wheel/tire balance issue. This is likely compounded by the fact that you're running much heavier AT tires which rarely are the smoothest tires at highway speeds.

With respect to brakes, rotors really don't warp. Over time, pad material imbeds itself in the face of the rotor. This material then create a grabbing point on the rotor by the pads. This grabbing creates a pulsating sensation often times referred to as a warped rotor.

There are basically three options here:

1) Bed the brakes. Being soft of the brakes all the time compounds this problem. Occasionally (once every three months or so), the brakes need to worked hard 3 to 5 nearly successive times to burn off that pad material on the rotor. In my cars and the 4Runner, I do 3-5 nearly successive 45 to 5mph panic braking, never fully stopping, and giving adequate time to cool the brakes after doing the panic braking. I typically do this in a vacant area.

2) Machine the rotor. If the pad material is really imbeded or is widespread, then you may need to machine the rotor to remove the material.

3) Replace the rotor and pads.