AjaxControlToolkit Slider's TextChanged event not firing

Hi,

I need for the slider to execute a code behind when users slide it and stop.  Somehow, the code behind method is not firing.  Does anyone have a solution?  Below is my C# code:

protected void CroplandSlider_TextChanged(object sender, EventArgs e)
{
  //get value from dropdownlist
  string huccode = ddlHuccodes.Text;
  
  //call the method
  DisplayScenarioPieChart(huccode);
}

ASPX:

<ajaxToolkit:SliderExtender ID="CroplandSliderExtender" runat="server">
  BehaviorID = "CroplandSlider"
  Minimum=-100
  Maximum=100
  BoundControlID="CroplandSlider_BoundControl"
  RailCssClass="croplandrail"
  HandleCssClass="croplandhandle"
  HandleImageUrl="~/images/sliders/corn_handle.png"
  RaiseChangeOnlyOnMouseUp="true"
  EnableHandleAnimation="true">
</ajaxToolkit:SliderExtender>

<div>
  <asp:Label ID="CroplandSlider_BoundControl" runat="server" AssociatedControlID="CroplandSlider"/>
  <asp:TextBox ID="CroplandSlider" runat="server" AutoPostBack="True" Text="0" BorderStyle="None" ReadOnly="true" OnTextChanged="CroplandSlider_TextChanged"/>
</div>

I can't figure out why the method is not firing when user stop sliding.  Appreciate any help.