Examining very large dumps

Hi, i just started the process of migrating from 7.4 to 8.3.1.
On restoring, apart from the easily explainable ERRORs (both in DDL, COPY), i got some ugly ERRORs
denoting foreign key constraint violations.
Since the dump is 35 Gbytes, i'd like your advice for examining, editing, extracting portions of large dumps,
in order to find the cause of the problem. vim (linux), vi (FreeBSD) or any other unix editor i tried, could not handle
the
volume.

Thank you very much for any help.
It's been the first day of the upgrade effort, and if i judge from the begining, the rest of the process will not be
anyeasier. 
--
Achilleas Mantzios