First of all, please close eventual ports on the API, those can be private and should not be accessible but from localhost.
What you need to ensure is a connection to the gateway nodes, or/and the network.
To do this you don't need necessarely to open port 5001 for incoming connections (UPnP enabled probably would help, but I am not sure this is already implemented... can anybody confirm/deny this?).
One thing you can try is to connect directly to a gateway and fetch the data from it.
For example, if you want to try Siderus gateway you can connect to it using:
curl https://meta.siderus.io/ipfs/connect.sh | bash
Unless that command fails (what it does is adding as bootstrap and connecting to nodes),
you should be able to download the content from the gateway:
Note: you can use also the browser to see the file.
The problem in loading now could be how slow the connection is to actually send the data from your local node to the gateway. That might affect if nobodyelse has the content you are trying to obtain from the gateway.