How do I troubleshoot why I have upload problems with speedtest.net?

How do I troubleshoot why I have upload problems with speedtest.net?

I have cable and I have historically been able to run speedtest.net without issues. Google seems to work fine, but other sites like my bank and facebook have intermittent connections. I run tracert and no really high pings. What other things can I do to troubleshoot my connection. The problem occurs on all 3 computers that I have (Win7 RTM, WinXP SP3, OSX 10.5)