When you use iptables, you are configuring the firewall, you are Adding a rule to the PREROUTING chain in NAT table, and the rule is: "all TCP protocol traffic with destination Port 80 (meaning that all incoming traffic
thru port 80) will take an action (-j takes effect if rule complies), what? REDIRECT that traffic to a port xxxx...Now, iptables redirects the traffic to port 10000 or 8080 or whatever the port you set.
Now, sslstrip will be in port 10000 (default) awaitting the traffic, if you set -l option in sslstrip, you can assign a diferent port.
Sslstrip start to act, disect the info and creates a favicon (if set that way), etc..Accordingly to what you configured in sslstrip.
Now, if it does not disect anything it could be because there is no info to disect in port 10000, 8080, or the port you are deviating the info to...sslstrip does its job, the thing is, there is no info there to disect..
Try to run nmap with -sC -sV -sS in your computer, check if the sslstrip is located at the port you set it. It should be listening there..If it is so, then info is not getting there..Try to analyze trafic with wireshark and filter port 80 and port 10000 (or the port where the sslstrip is listening at)...See what info you are getting..That is what I would do...
Hope this helps...