COuld possibly be bad right out of the box, I've had that happen to me with various auto parts. Try swapping it out with another from the parts store and see if it reads differently.
My buddy with an IS300 has said good things about these braces, now it looks like they are for the GS as well. But I haven't heard any feedback from the GS crowd. Was wondering if anyone here has tried them out.
SRT Rear Braces GS