There are three things to know about the "Cruise Mode" in Traktor (aka "autoplay").
1) Cruise mode can only be turned on while a song is playing.
2) Cruise mode will walk any active playlist.
3) Two options need to be enabled: "Load track at the end of current track" and "Stop deck at end of track"
After that, there are controls that allow a smooth/sharp transition and set the time for the crossfade.
See this for more...but you don't really need the fade in/out markers set, or the "sync" button pressed.