Download stalls at a certain percentage

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=290

Most commonly this is a problem with a router interfering with the download process.

You would need to bypass your router and plug directly into your modem and allow the game to download.

After the download you can replace your network cable to the router.

Also, if your router does not have the most updated firmware you may encounter this problem.

If you are still encountering this issue after bypassing your router please contact Support.