Hi,
you might try to create a Thread dump: http://community.jboss.org/wiki/ThreadDump
If you do this several times in the long "nothing happens" phase, you might identiy the bottleneck.
JBoss 4.3.0 is the EAP (commercial) version as far as I know. I am not sure about it, but I think it is based on JBoss 5.0 internally. So, you might try it with JBoss 5.1.0 or even 6.0. But I fear that migration to it might be a bit of a problem, because the 5.0 versions are much stricter on validation of xml deployment descriptors, and there is a big chance for library conflicts.
Best regards
Wolfgang