Bad Ping on multiple Clients

So I looked around, Googled, and I couldn't find anything all that helpful. I'm having a problem where I'm fine when I have one instance of WoW, but any time I launch multiple instances, the other instances have a significantly worse ping than the other instance. My main will have a ping around 100-120ms, but my other instances will be 1200-1500ms.

My internet should have enough bandwidth to handle multiple instances of WoW (speedtests are showing at least 25/20mbps)...so I don't know if this is common multiboxing issue and something I'm going to have to learn to deal with (I once played on a connection for a few months with a consistent 12,000+ms ping), or if this is something on my end I need to work out.