I had this problem too. I don't have the greatest DSL connection in the world and I made the mistake of buying the digital download because the local Gamestop and Walmart were sold out instead of driving to one further away to check. I bought the game on 10/11 and I just finally got everything installed on 10/15. It kept booting me when it would get 50-300 Mb in whenever I'd try in the afternoons in my time zone.

I managed to get it all in piece by piece by downloading overnight when I assumed both local network traffic and game traffic were off peak. Took me a while since I work nights and could only start it on days I had off, I leave for work when my connection is still iffy. The other two things that seemed to help were running the launcher as an administrator for the Windows version and anything I have in the house that used WiFi got shut off. Good luck!