There's a theme today it seems with data sharing between records when using database sources.
Accordingly, I have a two pass solution to recommend.
First, open your DBF file as you do normally. Build and run a project export from the Table windows to create a fixed-length text file. In effect, this will output the Table as a report file. Save the model and the project files for later reuse.
Now open the new text file as a conventional report and model it, employing the "Copy value from previous record" mechanism in the field properties. Again, save the model (and project if desired).
That ought to do it.