[2008] Loading File! Help Me Huge Problem!

[VB6Learner]

Hey I have made a HEX editor But im having one problem when I open A large file like 150KB Or over it takes a hour to load and if anything clicked it freezez is there any way to speed this up here is my OpenFileDialog code... And if I open the save one file with HxD (Different HEX editor) then Save it with mine some coding is different It only works when I save it with HxD does anyone know why?

Here is my Openfiledialog

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        If Me.OpenFileDialog1.ShowDialog = Windows.Forms.DialogResult.OK Then
            Me.TextBox1.Text = String.Empty
            Using streamReader As New IO.StreamReader(OpenFileDialog1.FileName, System.Text.Encoding.Default, True)
                Array.ForEach(Array.ConvertAll(streamReader.ReadToEnd.ToArray, _
                New Converter(Of Char, String)(Function(x As Char) Hex(AscW(x)).PadLeft(2, "0"c) & " ")), AddressOf Me.TextBox3.AppendText)

            End Using
        End If

    End Sub

Here is my savefiledialog

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox3.Text = TextBox3.Text.Replace(" ", "")
        Dim SaveFileDialog1 As New SaveFileDialog
        Dim sw As System.IO.StreamWriter
        With SaveFileDialog1
            .Filter = "Text files (*.txt)|*.txt|" & "All files|*.*"
            If .ShowDialog() = DialogResult.OK Then
                sw = New System.IO.StreamWriter(.FileName)
                sw.Write(HexToString(TextBox3.Text))
                sw.Close()
                sw.Dispose()

            End If
            SaveFileDialog1.Dispose()
        End With

    End Sub
    Function StringToHex(ByVal text As String) As String
        Dim hex As String = ""
        For i As Integer = 0 To text.Length - 1
            hex &= Asc(text.Substring(i, 1)).ToString("x").ToUpper

        Next
        Return hex
    End Function
    Function HexToString(ByVal hex As String) As String
        Dim text As New System.Text.StringBuilder(hex.Length \ 2)
        For i As Integer = 0 To hex.Length - 2 Step 2
            text.Append(Chr(Convert.ToByte(hex.Substring(i, 2), 16)))
        Next
        Return text.ToString
    End Function