rsterling,
The coreservername.txt file is only for remote consoles. It was needed so the boot media created on a remote console knew who the core server was (if I remember correctly).
Also, you need to have the same "name" in your template that you have setup in your preferred server configuration. e.g. if preferred server setup is server.domain.com and template is calling \\server\path (or the opposite), it will not work.
What do the client side provisioning logs say (maptopreferredhandler.log)
-Tracy