WPF moving border around on screen

I'm making a game inventory system where I have a grid and borders that take up a grid space have a background image of the icon. For example in grid position 0,0 I have a border with a background of a health potion. I want to be able to drag this border to any other grid location. Right now I'm working on just clicking and dragging the border to follow the mouse.

What I have so far sort of works but not really. If sort of freaks out when I left click on the icon and move slowly. However I can move out of the icon fast and it doesn't keep up so it then stops moving until I'm back over it. Any ideas on how to get this kind of functionality?

public partial class MainWindow : Window
    {
        TranslateTransform trans = new TranslateTransform();
        Border border;

        public MainWindow()
        {
            InitializeComponent();

            // create a broder and set it's background image
            border = new Border();

            border.Visibility = System.Windows.Visibility.Visible;
            var img = (Image)MasterGrid.FindResource("notepad");
            var imgBrush = new ImageBrush(img.Source);
            border.Background = imgBrush;
            border.Margin = new Thickness(2.0);

            // add the border to the grid
            Grid.SetRow(border, 0);
            Grid.SetColumn(border, 1);
            Grid.SetRowSpan(border, 2);
            Grid.SetColumnSpan(border, 1);
            InvGrid.Children.Add(border);

            // hook up events
            _00.MouseUp += new System.Windows.Input.MouseButtonEventHandler(_00_MouseUp);
            border.MouseDown += border_MouseDown;
            border.MouseMove += border_MouseMove;
        }

        void border_MouseMove(object sender, MouseEventArgs e)
        {
            // make the border follow the mouse position
            trans.X = e.GetPosition(border).X;
            trans.Y = e.GetPosition(border).Y;
        }

        void border_MouseDown(object sender, MouseButtonEventArgs e)
        {
            border.RenderTransform = trans;
        }

        private void _00_MouseUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            MessageBox.Show("test");
        }
    }