ItemsControl missing vertical scrollbar

ItemsControl by default does not wrap ItemsPresenter in ScrollViewer so you have to do it manually like so:

<ScrollViewer Grid.Column="0" Grid.Row="1">
   <ItemsControl x:Name="tStack" ... >
      <!-- .... -->
   </ItemsControl>
</ScrollViewer>

Wrap your ItemsControl in a ScrollViewer control.

<ScrollViewer VerticalScrollBarVisibility="Auto">
  <ItemsControl ...
</ScrollViewer>

Remember to put the Grid.Column="0" Grid.Row="1" attributes in the ScrollViewer instead of in your ItemControl.