First of all, make sure that LW's being allowed through the Windows firewall.

Try updating your Java to the latest version. Download the JRE offline installer & remove any other Java versions on your computer, before you install the new one.
Java SE Downloads

When you set up port forwarding, did you use these instructions?
Port Forwarding for the Dlink DI-604
Did you make sure to set up a static IP address on your computer first (there's info about how to do that in the instructions above)? Also, make sure that LW's listening port, port in the 'manual port forward' box & port forwarded within the router are all the same number

Xplornet are known to throttle bandwidth for p2p but a few other people have had connection problems as well. Most of those had satellite connections though, so I'm not sure about wireless.
You could try changing ports. In LW tools > options > advanced > firewall config. Change LW's listening port to something in the range of 49152 - 65535 (eg 65000) > apply > ok. If you change ports, you'll also need to change the port number forwarded within your router's configuration.