Increase Textbox Character Limit

I am working in Office 2000, and have 3 Textboxes, I need to copy text from Textbox1 and Textbox2 to Textbox3, and the code below works but only when the character length is limited. I need to be able to show much more text. Suggestions. I am trying some of the code

Option Explicit
Sub Text_Copy()
Dim ch1 As Characters
Dim ch2 As Characters
Dim ch3 As Characters

With Sheets("Aim Up Description")
Set ch1 = .Shapes("TextBox1").TextFrame.Characters
Set ch2 = .Shapes("TextBox2").TextFrame.Characters
End With
With Sheets("Description Summary")
Set ch3 = .Shapes("TextBox3").TextFrame.Characters
End With
ch3.Text = ch1.Text & " " & ch2.Text
End Sub

I have found code on other posts that I have tried (like, Range("A16").Value = Val("TextBox1"),