How many incomplete files do you have?

You can do some quick tests; go here & do as many of the following tests as possible. Particularly: Tweak Test, speed test, Line Packet Loss Testing. http://www.broadbandreports.com/tools There's something blocking LW! I suspect the issue is either (still) SP2 or your ISP line is unreliable. Or you haven't configured your firewalls properly.
There's no need for any individual to have SP2!!! It was intended for big businesses that run major networks. But it has even caused them major problems. So for individuals to update to it is adopting problems you really didn't need b/c it doesn't serve any purpose for you.