I have a dedicated windows 2003 server at a colocation facility that i use for game server hosting. Over the past 7 months, packet loss has become horrible with random periods of massive lag. My host says it's something on my end. I use a firewall with SPI enabled. Could that be causing it?

Strange thing is, the first few months my server was at that colo, they only had around 40 other servers on a single OC-192 pipe and i never had packet loss despite having the same SPI firewall. But now they have over 300 servers on the same OC-192 pipe. Could the packet loss be caused by my SPI firewall or them overloading the network with servers?