Irule simple redirect or not?

Another thing that would cause a 504 is a TCL error if you have other iRules applied to that virtual server and they are both trying to send a response or a redirect. Since it can't do both the F5 will not reply and will show a TCL error in /var/log/ltm. If that is not the only iRule applied to the virtual server then you may want to check the logs (and the logic). The iRule I posted earlier is exactly what we use in production, so it alone should give a 301. The other virtual server may have issues with the request, so I recommend using Fiddler to check the responses.