There is a beta firmware to solve the problem. In next new firwmare, it will be added... You can downgrade the old firmware or ask for the beta firmware from TP-LINK support team if it is urgent......

You can upgrade the latest firmware first. If the problem is the same, do you have APN, Dail Number, username and password from your ISP? Try to input those information manually....

If you installed the utility, go to Advanced and select Audio or Video instead of Internet to test. Check the Rate under Network. Did you ever use some other powerline devices but no such a problem...

How about PA8030P? It has 3 ethernet ports, it has passthrough feature and it is more stable. If you need three, you can buy 1 kit(two) plus 1 single....

As I said, after reset, you have to reconfigure the router to work with the modem. Can you login the router page now? The modem shoulde be connected to WAN port and PCs should be connected to LAN...

When WMM is disabled, it will work in 11G mode. Thus, the maximum speed will be 54Mbps. http://www.smallnetbuilder.com/wireless/wireless-features/30938-dont-mess-with-wmm