Do you store your files inside the database or externally? What hardware are you using? Do you have enough space on your hard drive?
Secure storage will make things go a tiny little bit slower, but I do not think that is your problem
Check your firewall settings (especially windows built in software firewall on the server). According to this knowledge base article, is port 443 used to upload files to contaner fields. If that port is closed, there will be a time out before using port 5003.
(You might need to open port 80 as well.)
With best regards Magnus Fransson.