Brake shake at 60+mph

Changed out rotors and pads about 4 months ago on my 99 classic 4x4 and all was good initially. I'm now getting a brake shudder at highway speeds, which will smooth out with additional pressure down to a stop. The shudder is really there when braking down from 70 to 55, or so. Any ideas? Could the pads be sticking on the knuckle until additional pressure from the pedal smooths them out?

Thanks, mike

In my experience high speed shudder that goes away is due to the beginning of warp.

Thanks. I suspected that as well. I'll pull the rotors and swap them out - having the lifetime warranty comes in handy.