I was having the same issue and this works excellently.
Private Sub DataGridView17_CellFormatting(sender As Object, e As System.Windows.Forms.DataGridViewCellFormattingEventArgs) Handles DataGridView17.CellFormatting
'Display complete contents in tooltip even though column display cuts off part of it.
DataGridView17.Rows(e.RowIndex).Cells(e.ColumnIndex).ToolTipText = DataGridView17.Rows(e.RowIndex).Cells(e.ColumnIndex).Value
End Sub