Thanks All for your responses to my original post !
Apologies, I tried to describe the issue but the term "shuddering" I used may have thrown readers to conclude it was a warped rotor. It is not related to the rotors, I am super familiar with rotor issues and have been replacing and working on all my cars brakes since the 1980's.
The issue I have ( and it is true of 4 Runners I have rented on trips) is when the brakes are applied firmly at speed they are "grabby" ( better term?) . Frankly , its a bit disconcerting . The brakes stop the vehicle in a straight line , so the effectiveness of the brakes seem fine. But that "grabbiness" is just weird. Almost a sense of a loss of control for a brief moment. Now maybe it is the ABS kicking in or something. That said, I have owned ABS equipped vehicles since 1990 ( Volvos; Toyotas; Corvettes). Perhaps as another reader commented, the TRD braking system is tuned for "offroad" and the compromise on the road is what I am feeling?
Frankly , my old 2002 Sequoia has a better braking system than my 2015 TRD . Again, I have noticed exactly the same issue on two other non TRD 4Runners that I have rented .
Not sure whether I am using the right term to describe the issue and maye it is just the brakes are too effective. I am pretty certain it is a engineering/design related issue specific to the 4Runner ( and maybe all newer Toyotas?).