Just curious, but I know from experience that Norton stuff is the hardest thing to remove once it's installed. There's a special program on symantec's web site to really remove it completely, so you could try downloading and running that.
Check out
PCPitstop, they have full pc test you can run that'll check everything from hard drives to internet connection and tell you if there's any problems. You can check anonymously if you don't want to create a login and all that...
Of course, emptying your temp internet files and cookies, etc, might help, if you haven't already done it. Windows firewall is a pain in the ass...I would definitely recommend dumping for another one if you can, I had connection problems left and right before I disabled it.