GT5 Servers appear to have been restored to a fairly robust state, at least slightly better than before the recent 'issues'.
Here's a few tips - Find out your ISP's Domain Name Server(s) IP address (DNS). Set your PS Internet connection manually and set the DNS numbers in the 'specified DNS' (i.e. DNS = manual), and enable UNPnP and test it.
Is your PS is wired to a router? Not wireless?
Also, clearing your cache before you go in to the GT Life area or join a lobby helps, too. (Options, Network).
Also, if the room is set with race quality = high, and voice quality = low, this helps bandwidth issues, too.
I apologise in advance if you feel I'm patronising you in any way. Just trying to help.