highlight duplicates

Try this code

Option Explicit

Sub highlight_dups()
Dim j As Long, i As Long

Application.ScreenUpdating = False

With Worksheets("Sheet1")
    For j = 2 To 5
        For i = 5 To 30
            If .Cells(i, j).Value = .Cells(i + 1, j).Value And .Cells(i - 1, j).Value <> .Cells(i, j).Value Then
                .Cells(i, j).Font.Color = RGB(255, 0, 0)
                .Cells(i + 1, j).Font.Bold = True
            ElseIf .Cells(i, j).Value = .Cells(i + 1, j).Value And .Cells(i - 1, j).Value = .Cells(i, j).Value Then
                .Cells(i + 1, j).Font.Bold = True
            End If
        Next i
    Next j
End With

MsgBox "Done"

Application.ScreenUpdating = True

End Sub