If you run tcpdump on the external interface do you see the packets coming in on port 55555?
You either need a friend to ssh in to your box, or use a free shell account provider like
http://silenceisdefeat.org, to ssh in to your box. Remember that the connection really does need to enter the external interface through the internet.
Please read
http://openbsd.org/faq/pf/rdr.html#reflect why connections initiated from the local lan will never get redirected