Portal system very slow

You will need to be much more explicit here - what do you mean by "errors being thrown from the application"? Do you mean TCP Resets? I have seen issues like this where the server performs redirects and causes issues.

My suggestion is to capture a session with a single client on both the client and server side of the f5, check for resets, redirects, 404s, etc. You can use the tcpdump and ssldump commands ( use -p with tcpdump if you have recent software )