You are experiencing Packet loss more than likely. If you are on CABLE MODEM, contact your ISP and let them know to check your NODE for noise levels in the lines, this will cause the CM to drop packets with no TCP recovery, then everything will start to fall apart. A connection under these conditions can easily LOOK OK, but NOT be OK. Conduct a ping test, run COMMAND PROMPT (Use WIN+R then type CMD, press enter) at the prompt type the following (without the quotes)"ping cisco.com -4 -t", let this run for 10 minutes then hit CTRL+C while focused on the CMD Prompt window. Copy the Results and paste them back...
Thanks!