I experience these symptoms when another PC on my network is using all of my bandwidth. Granted, I have very little bandwidth available, and I doubt you're on DSL like me. ;p Still, I would investigate whether or not there is something on either computer eating up resources. Does this issue occur when only you are playing the game, and not your partner? Check Resource Monitor in Windows to see which applications are connected to the Internet, and if anything looks out of the ordinary there.