I've used the following technique when needing to access large multi-line text fields for reporting purposes: -
1) Create a new View containing a Repeating Table, name one of the columns something like "myTextField_Output"
2) Set this column to be multi-line with paragraph breaks
3) Set the Default value of this column to be the multi-line text field on your main form
4) Promote the "myTextField_Output" field and use the Merge option
5) The field will now appear in the SharePoint form library as a multi-line text column