I am willing to bet that these 2 issues are 75% (give or take) of the problems people are having with uploading or downloading!

The correct ports are not enabled on these routers!

I have a Netgear gateway router, and tried 3 different file sharing programs (including this one) without the router and found little if any problems!
With the router, either the program wouldn't connect to the net in the first place, would only download 10% of the requested downloads or wouldn't upload anything!

I don't know much about firewalls, other than I don't use or want to use them, BUT they are another program to run, another program to setup, and another program to go wrong and cause problems. Yes they protect you, BUT at what price?