Are we talking about trouble sending a file or receiving one?
When you send a file, then you are uploading it, and you would see a number of bytes sent.
When you receive a file, then you are downloading it, and you would see a number of bytes received.
When you set the ports on the new router, did you use instructions for that router, or did you just use the same as on the old router?
If you just used the same settings, then they might not be set correctly for the new router, though you think it is.