How new is the turbo. Its unlikely but there is a chance your wastegate housing could be cracked. When mine went i noticed a lack of boost and it got to the point where i actually took the screw completely out of the bleed valve and it wouldn't boost higher than 10psi peak but dropped down to 6psi higher up the revs.

It was worth a mention but seeing as yours is boosting higher sometimes the actuator seems more likely.