I have a gt2871r as well and it had some shaft play from the factory. It concerned me at first because I expected virtually none. The shaft play i had is what you are calling up and down play, but I didn't have any of the back and forth play. Do you have any other turbos to compare it to or any other experience with other turbos to compare it to? Either way, I guess, I would do what nismo94 suggested and send it back if you think its excessive.
'96 200sx SE (Hopefully a G37 soon)
'92 240sx SR20 workshop