After updating the drivers, did you try to set the refresh rate to 60?
Another attempt would be to first uninstall all of the nVidia drivers through Control Panel->Add/remove Programs, reboot and reinstall the latest ones. If still no avail, using some driver cleaner to really get rid of any old drivers might do the trick.
And as Skuzzy asked, cables... Are they well seated, does twisting them change anything, have you removed them lately and accidentally twisted a pin while replugging?