It turns out that the gpu tweak II actually DOES save your custom fan curves. The problem is that this program is kinda glitchy, however the solution is rather simple and it always work. -> Make your custom profile and set up your fan curves, then save. Obviously it stays that way UNTIL you click away on another profile or if the program restarts. When that happens, simply click away from the custom profile to another(w/e which one), then click back on your custom profile and check your setup, it's all back the way you set them up.