problem while setting refresh rate in xorg

[freenity]

Hi.
I have just installed the nvidia drivers on my FBSD6.2 i386. It work fine
but I cant set my refresh rate at 75, it sets at 50 with a resolution
1280x1024. The monitor is LG Flatron L1740B and my video card is Geforce
6100.
Here is my xorg.conf file:
Thanks for any help.


Section "ServerLayout"
        Identifier     "X.org Configured"
        Screen      0  "Screen0" 0 0
        InputDevice    "Mouse0" "CorePointer"
        InputDevice    "Keyboard0" "CoreKeyboard"
EndSection

Section "Files"
        RgbPath      "/usr/X11R6/lib/X11/rgb"
        ModulePath   "/usr/X11R6/lib/modules"
        FontPath     "/usr/X11R6/lib/X11/fonts/misc/"
        FontPath     "/usr/X11R6/lib/X11/fonts/TTF/"
        FontPath     "/usr/X11R6/lib/X11/fonts/Type1/"
        FontPath     "/usr/X11R6/lib/X11/fonts/CID/"
        FontPath     "/usr/X11R6/lib/X11/fonts/75dpi/"
        FontPath     "/usr/X11R6/lib/X11/fonts/100dpi/"
EndSection

Section "Module"
        Load  "dbe"
        Load  "dri"
        Load  "extmod"
        Load  "glx"
        Load  "record"
        Load  "xtrap"
        Load  "freetype"
        Load  "type1"
EndSection

Section "InputDevice"
        Identifier  "Keyboard0"
        Driver      "kbd"
EndSection

Section "InputDevice"
        Identifier  "Mouse0"
        Driver      "mouse"
        Option      "Protocol" "auto"
        Option      "Device" "/dev/psm0"
        Option      "ZAxisMapping" "4 5 6 7"
EndSection

Section "Monitor"
        Identifier   "Monitor0"
        VendorName   "Monitor Vendor"
        ModelName    "Monitor Model"

        HorizSync        40-80  #60
        VertRefresh      50-90  #75

EndSection

Section "Device"
        ### Available Driver options are:-
        ### Values: <i>: integer, <f>: float, <bool>: "True"/"False",
        ### <string>: "String", <freq>: "<f> Hz/kHz/MHz"
        ### [arg]: arg optional
        #Option     "ShadowFB"                  # [<bool>]
        #Option     "DefaultRefresh"            # [<bool>]
        #Option     "ModeSetClearScreen"        # [<bool>]
        Identifier  "Card0"
        Driver      "nvidia"
        VendorName  "nVidia Corporation"
        BoardName   "C51 PCI Express Bridge"
        BusID       "PCI:0:5:0"
EndSection

Section "Screen"
        Identifier "Screen0"
        Device     "Card0"
        Monitor    "Monitor0"

        SubSection "Display"
                Viewport   0 0
                Depth     16
                Modes    "1024x768"
        EndSubSection
        SubSection "Display"
                Viewport   0 0
                Depth     16
                Modes   "1280x1024"
        EndSubSection

EndSection