I found the delay was actually coming from the browser, not the pfSense box. By removing the exceptions for the self signed certificates in the browser, and re-accepting them, all is good now and pfSense GUI is back to running fast. I'll keep an eye on it and post if anything comes up.
This is an issue from Firefox 31 (I guess you were using Firefox). There are other threads about this also. In Options, Security you have to View Certificates and delete all the ones listed under "Company Name" - those are the "unknown" ones that you have previously added as exceptions in the past. Then things speed up again.