Remote Cisco 7961G Not regerstering

Hello everyone! Happy Friday!
I have been maintaining a FreePBX system for a client for about 5 years now. A little back ground info: have rebuilt the system from the ground up as it was horribly outdated within that time, and have kept it updated regularly. They have been utilizing Cisco 7960's which have stood the test of time with little to no issues. However without consulting me the owner purchased a 7961G to be used as a remote extension. While I have already configured a 7960 for a remote extension successfully and works great! This 7961G is giving me all kinds of headaches. The first being it utilizes XML files instead of the simple text based files. I flashed it to the current firmware for SIP protocol, configured the extension with the correct password in FreePBX but when I attempt to register it from home, it connects successfully pulls the config.xml files successfully from tftp but when registering I can see in the logs that it registered successfully then a second later I get an error registration failed. However I can make calls with no audio, but do not receive them from followme ring plan. In FreePBX the phone remains marked as unreachable. I have tried configuring my home modem with the same settings I used to set up the 7960 remotely which have not worked. Does anyone have any suggestions? I keep thinking its a firewall and NAT issues, but I've tried every setting I can think of. I appreciate any input, and thank you in advance.