How I can do to keep my 1440x900 74 mz configuration after reboot?
After configuring it in NVIDIA settings and reboot, it returns to previous 60 hz.
Thanks in advance for your help.
Use gksu nvidia-settings as suggested in the comments
Once you have adjusted your settings, click the "Save to X Configuration File" button. When asked if you wish to merge your changes, say no.
Make sure the "Merge with existing file" box is unselected.
See https://help.ubuntu.com/community/NvidiaMultiMonitors#Saving for details.