Had the same problem only when going down mountain passes and applying slight braking. A shudder would develop as soon as the disks warmed up.
Solved it by fitting a new set of disks from Power Brake.
Apparently it can also be from deposits from your pads on the disks. Abuse them by going to 100km/h and braking hard down to 40km/h 5-6 times. This should make them hot enough to burn away any deposits
2006 Patrol 4.8 GRX Tiptronic Y61/GU(4)
ARB Bullbar, TJM 2" Suspension, Snorkel, 285/70/17 BFG KO2's, 40L Engel, Nuvi 1410, TPMS, SatNav
Stop Rhino Poaching Supporter!