For the example you posted, what makes it non-unique? Is it that the tbl_refnum is the same, butcarrier is different, or that pronum is different? Or is this a case where the data is unique because carrier is different? Not sure if this will work for you, but you might try this.
SELECT LTL FROM TheTable GROUP BY LTL HAVING COUNT(*) > 1If that does not give you what you want, post some sample data that includes unique records and non-unique records and the expected output you want to see.