Edit grub video resolution

Change grub resolution:

sudo subl /etc/default/grub

Edit (run videotest from grub via c to see supported)

GRUB_GFXMODE=1024x768x32

Rebuild grub with this or equiv

sudo grub-mkconfig -o /boot/grub/grub.cfg

In the same file you can change the default text resolution by appending the res to this line

GRUB_CMDLINE_LINUX_DEFAULT="quiet resume=UUID=75a2dd2e-c8d0-4400-a8c8-182ae551cb8d video=1600x900"

Rebuild grub