Yep it looks like port forwarding will be needed for your router. If you use LW on both then you'll need to forward a different port number. 2 computers can't use the same port for same program.

I am surprised about the issue still not being solved once the router was taken out. You're using cable which I believe can be affected by local users (ie: peak time use.) But that doesn't explain the very slow speeds. I would recommend you do your tests for LW using the magnet links Stief recommended. Those have very fast sources.

As for speed tests, yes they can be affected by many things including how many people are using the same test simultaneously, the location, etc. But the link I gave you does give option to try speed tests from different locations.