Home Network :: Wireless Router Significantly Slowing Down Internet?

I have cable internet with a speed plan in the 10-15 mbps range. I have a wireless Belkin g router that is several years old. Connected to the router I have my cable modem as well as my PS3. I connect wirelessly from my PC to the internet, as my PC is in the other room (more on that later). When I'm streaming movies via WiFi to my TV, the connection is highly unstable. Some days, I will not experience any stuttering (or very minor stuttering), whereas other times the stuttering is almost unbearable. Last night, I had trouble streaming a DVD quality movie whenever it went above 2 mbps total bitrate. Other times, I can stream HD movies without much stuttering (except for very action packed scenes).Interestingly, I stream Netflix movies over my PS3 via a *wired* connection. Last night, I conducted a speed test on my PS3. First, I had the PS3 plugged into the wireless router. I achieved speeds around 2 - 4 mbps on average. I then plugged my PS3 directly into my modem and achieved speeds around 10 mbps! The boost was instantaneous. I should note that on my PC, I speed test regularly over the WiFi and achieve around 4-6 mbps on average (only once did I achieve 11 mbps).