Anisotropic filtering settings do not change shimmering.
Using Oculus particularly at Philip Island in pit stall.
On fencing and wall.
How do I lower shimmering?
Hmm, do you mean flickering instead of shimmering? Anyway, anisotropic filtering isn't relevant to any of them. My best guess is that it's probably a z-fighting issue which can be usually amended by either increasing z-buffer bit depth, or (since it's not an option in GPB) by reducing the max drawing distance. Btw, I use oculus for about a year now and haven't had any issues with GPB so far.
Try downloading the latest drivers for your gpu, and see if you can force 32-bit Z buffer in its control panel.