How to change gdm screen resolution?

[shadowkernel]

Hi,

My default screen resolution is 1400x1050, and in gdm greeting screen, 
the screen resolution is always 1024x768 (xfce and gnome sessions both 
work OK). The fonts seems a little blur. My video card is Nvidia Quadro 
NVS 140M, and I have installed the newest nvidia driver with version 
169. How to change the gdm settings to the LCD native resolution? I have 
tried 'sudo dpkg-reconfigure gdm', but it does not work. By the way, can 
anyone provide me with the boot sequences of Ubuntu? It seems that 
Ubuntu is different from other distributions, as 'teinit' does not work. 
I want to know what configuration files gdm reads. Any websites or pdf 
files are welcomed. Thanks!

Best regards