I had a problem with the waste gate stem that is attached to the puck was getting carbon build up in the sleeve it runs through. There is no bushing or anything there and it would bind up usually partially open and caused a low boot issue like that.
I had to take the DP off and remover the waste gate assembly and open up the hole.....problem fixed.
Take your actuator arm off of the waste gate, it should move back and forth very easily.