How/Where are you preloading the modules? Are you using Apache::DBI? If you are make sure it is loaded before any DBI calls including the loading of.

Setup perl-status

<Location /perl-status>
  SetHandler perl-script
  PerlHandler Apache::Status
  order deny,allow
  #deny from all
  allow from all # adjust for your IP
</Location>
[download]

and preload Apache::Status BEFORE Apache::DBI, if you haven't already. That will allow you to confirm that Apache::DBI is caching the DBI connects and you can see what modules are loaded into memory.