OK here's the latest update. I dynoed it again tonight and the wastegate actuator I replaced works fine......BUT...... because I have a custom twin dump pipe, the wastegate doesn't flow well enough to regulate the boost. As such I get a runaway boost condition even though the wastegate is open.
The solution is to get another dump pipe made up though this time there won't be a separate pipe for the wastegate outlet. My tuner says he's never seen any power gains from having a twin dump pipe anyway, so I won't see a loss in power.
Attached is a graph showing the boost creep.
I'm still planning on going to open practice at EC on the 20th so I'd better get cracking at getting my exhaust guy to make a new dump.