Here is a way to fully remove the double for loop, multiple array, split and concatenation issue. Simple and working.

    Public Shared Function Truncate(ByVal Input As String, ByVal intMaxLen As Int32) As String

      If Input Is Nothing Then
        Return String.Empty
      End If

      If Input.Length <= intMaxLen Then
        ' no need to truncate
        Return Input
      End If

      ' search for last space before max lenght
      Dim iCutAt As Integer = Input.LastIndexOf(" "c, intMaxLen)

      Dim inputCut As String
      If iCutAt = -1 Then
        ' there is no space so cut anywhere
        inputCut = Input.Substring(0, intMaxLen)
      Else
        inputCut = Input.Substring(0, iCutAt)
      End If

      Return inputCut + "..."

End Function

I haven't done any benchmark but it's probably 100 times faster for both long and short input string.

Running InstantASP forum with many code change.