I have 16GB of VRAM, but Ghost of Tsushima is still dropping frames at 4K on my RX 9060 XT, what's wrong?

I've got 16GB of VRAM, yet my FPS was jumping wildly between 40-60 at 4K—it felt like my GPU was dancing disco on my screen. The Vastarmor RX 9060 XT's memory bandwidth was hitting a wall with ultra-high-res textures, with effective utilization dropping by 12-18%, leaving the GPU core idling while waiting for data. I tried dropping to 2K, but the loss in visual fidelity was just pathetic and not an option. I went into the AMD driver settings, switched the memory management to 'High Performance', and cleared out 4GB of shader cache. In stress tests, the minimum FPS rose from 32 to around 45-48, and the stuttering became much less frequent. I actually accidentally triggered an overclock setting during the process which crashed my driver, but a clean reinstall fixed it. Temps are sitting at 68-74℃. I've backed up the optimized driver config via a system image tool.