Do you have the following directory on your system?
/etc/X11/xinit/xinitrc.d/
Here, I have this file in it:
/etc/X11/xinit/xinitrc.d/95-nvidia-settings
with the following contents:
#!/bin/sh
/usr/bin/nvidia-settings --load-config-only
And it works just fine. However, it’s important that the file is marked as executable, so do:
chmod +x /etc/X11/xinit/xinitrc.d/95-nvidia-settings