Manoy, I don't understand why you took off the router. IF you put a hub, did you use a firewall?
Well, file transfer thru NAT router does work. tomshardware has a guide how to enable. Now, I don't have Upnp enabled. nor I did the routing for those ports and I can still send files to my work (NAT to NAT) so I don't see a problem with that.
If you see slow connections make sure you don't have any computer in the DMZ, that could be compromised (hacked)
Install temporaly a firewall in all of your computers to see what is going on with your network. You might have a trojan or worm. At least like that you can pint point the source. If that still doesn't work, reset the router to factory defaults.
I am tending right now to believe that your security was compromised when you went back to the hub, either from a hacking or virus-type.
What router do you have?