Could be any manner of things chap, my first thought when i read your first post was the Actuator, but you say you've already eliminated that. Can you give us a bit of history on the car, did you buy it recently with those bits fitted, or have you had the car for a while and fitted those bits, did it ever feel faster and seem to boost more???
What i do to set the actuator is get a foot pump and a connector, plug it into the hose and set the load on the wastgate to see when it starts moving, that way you know that it's set correct. Failing that, it could be an air leak or a duff turbo that just can put out the correct boost. From experience the car with a stage 3 chip should safely be able to boost around 1.5bar and upwards if you really get bored and fancy your chances, if the fuelling has been set etc..
I'd check all your hoses/clamps and intercooler for anything obvious.