Skiman, it might not be overboost cut, are there no reputable tuners near you who could diagnose?

To adjust the actuator you really need to remove the heatshield, and then ideally you need to unclip the actuators arm from the wastgate (otherwise you could possibly damage the diaphragm in the caspule if you just slacken the nut, and twist the rod), then adjust, refit, test etc. but again, you really want to be doing this with an accurate psi boost gauge. As you can imagine, it gets real hot in there if you need to re-adjust!

Skiman - check all the small bore boost pipes are still attached......