DD-WRT is an open source alternative for wireless routers. It doesn't work on all routers, but the list it supports is very large. Many people switch to using DD-WRT because it offers many more and improved features of the standard factory firmware that comes with your router. I used DD-WRT for a long time and loved it. That is, until I started using Ooma and needed to set up QoS. I now use Tomato which is another open source firmware for wireless routers and it is perfect. I asked about DD-WRT because when I used its QoS it also gave me the random and poor quality of service measures similar to what you observed in your tests.
QoS stands for Quality of Service. This is a networking concept used to tweak that your network usage works just the way you want it. Let's create an example where there are several people using your Internet connection. Like if you're in college and have a couple of roommates. One of them runs a server for sharing MP3s to the world, the other downloads tons of stuff, another is always gaming on their XBox 360, and you just want to surf the net and read email. When people are downloading like mad from roomy 1, the XBox gamer and you will feel the internet is very sluggish. The gamer will be the most upset because his lag time will cause him to get killed a lot. Using QoS on a router (if it supports it) you can give file sharing protocols like Bit Torrent a very low priority, give web surfing a medium to medium high priority, and give gaming the highest priority. What this does is allows the gamer to feel like he owns the Internet connection regardless of what others are doing. His game play experience will always be perfect. Your web surfing will always feel snapping, and the file sharing doesn't matter since it takes such a long time no one will ever notice anyway. That is what QoS gives you.