Attempt to change resolution on Grub

Today after search, I was try to change the Grub resolution , because on 'auto' it drops low. My monitor, native support 2560x1440. On login screen is well set as on OS when loading too.
I tried to change it through sudo micro /etc/default/grub , it pop up the Grub parameters . After that , moved to GRUB_GFXMODE line, and edit from auto to
After exit I typed on konsole
sudo update-grub
But the parameter isn't saved, still show as 'auto' only after reboot. Plus I think it give some small error now when load Grub but it loading the default one so no issues, I can login normally still
So my question is : How I will save the edited resolution? Or isn't support 1440p?