Are you have:
- Enabled
VirtualizingStackPanel.VirtualizationMode
for a Grid? if not – try to set. - Set VirtualizingStackPanel.IsVirtualizing=”true” for DataGrid
- Wrapped up a Grid by a StackPanel container? If yes – try to remove.
- Wrapped up a Grid by an external ScrollViewer control? If yes – try to remove.
One more point,
could you bind whole items collection at once instead of adding each item into the grid.Items collection?