Comment 7 for bug 92599

I think we got the guilty :)
Thirst of all, sorry to have confused you. By hardware I didn't mean an hardware failure but an hardware limitation (I was thinking about the single link TMDS, but that was a false lead).

Now, in line 2404 you will see that your driver (note, this is the nvidia proprietary driver, which is, afaik, not supported by ubuntu) selects the 1280 x 1024 @ 60.0 Hz as the best fit to your specification.

Why is that, I can only guess, but you will see in line 366 that your driver EDID probing only detects a maximum pixel clock of 140 MHz: in principle this would mean that you could not use a resolution of 1280x1024@75 Hz which requires a pcf > 150 MHz.

You can try (AT YOUR OWN RISK) to override the EDID and check that you have the resolution/frequency you like, by using either of these options in your xorg.conf file (either in the Screen or Device sections):

Option "IgnoreEDID" "true"

This will disable probing of EDID from your monitor.

Option "ConnectedMonitor" "DFP"

This will override what the NVIDIA kernel module detects is connected to your video card.

Hope it helps.