Road cranks, road BB shell, so it should work without any spacers... But it doesn't! My friend has exactly the same problem with his own cranks, also GXP, 68mm, road cranks...
They need a lot of force. Mine have play until they're about as tight as I can possibly get them with a hand held allen key. Still spin freely and smooth though
are you using mtb or road cranks?
the video cleared everything (almost!) up for me
https://www.youtube.com/watch?v=D1UHtUt_V2Q