Gnome shell can't save screen resolution

Probable Cause

I assume that your monitor reports the high screen resolution as being preferred; unfortunately this information is used by GNOME Shell on each login to reset the resolution.

How to Fix

I had the opposite problem: my monitor reported a lower preferred screen resolution (1280x1024) than the one I wanted to use (1600x1200). The fix I have used will hopefully be applicable analogously to your problem, though. Here’s what I did:

I ran xrandr -q to find out what the current preferred screen resolution is and what other screen resolutions (or rather “mode lines”) are available. In the output, the mode line marked with a + is the current prefferred one. It also matched the currently used one (marked with a *). Here’s the output for me (abbreviated):

Screen 0: minimum 320 x 200, current 1280 x 1024, maximum 8192 x 8192
DVI-0 disconnected (normal left inverted right x axis y axis)
DIN disconnected (normal left inverted right x axis y axis)
DVI-1 connected primary 1280x1024+0+0 (normal left inverted right x axis y axis) 352mm x 264mm
   1280x1024      85.0*+   75.0     60.0  
   1920x1440      60.0  
   …  
   1600x1200      85.0     75.0     70.0     65.0     60.0  
   …

To override the preferred screen resolution, I have created the file /etc/X11/xorg.conf with the following content:

Section "Monitor"
    Identifier "DVI-1"
    Option "PreferredMode" "1600x1200"
EndSection

As you can see, I took both the monitor identifier DVI-1 and the new preferred mode line name 1600x1200 from the xrandr -q output. You should replace these values according to your own setup.

After a logout (or reboot), the new preferred mode line was automatically used for both my display manager and for GNOME Shell. The new (abbreviated) output of xrandr -q was the following:

Screen 0: minimum 320 x 200, current 1600 x 1200, maximum 8192 x 8192
DVI-0 disconnected (normal left inverted right x axis y axis)
DIN disconnected (normal left inverted right x axis y axis)
DVI-1 connected primary 1600x1200+0+0 (normal left inverted right x axis y axis) 352mm x 264mm
   1600x1200      85.0*+   75.0     70.0     65.0     60.0  
   1280x1024      85.0 +   75.0     60.0  
   1920x1440      60.0  
   …