In this case to assist you further could you please help me with the modem Firmware version mentioned on the modem GUI.

I advise you to retrieve the IP address for the second port by contacting your internet service provider.

I suggest you to set up link aggregation by following the instructions below after obtaining the second IP address:

http://arris.force.com/consumers/articles/General_FAQs/SB8200-Link-Aggregation-Setup

that’s not the point of “WAN link aggregation” from a modem. you dont need 2 ip addresses. You only have one in with the coaxial then. The point of WAN link aggregation is one line in with coaxial that provides a 1-2 GBPS connection then you connect the TWO 1 gbps lines from your modem to your router then creating a > 1 gbps connection by combining those two 1 G lines into one stream (aggregation). In my case I have 1.4 gbps from Xfinity then the LAG from the modem aggregates the two 1 gbps speed together in the router to get the full speed of 1.4 gbps. The reason for this is because my router only has 1 gbps on the “in” WAN ports. (1 being the WAN and another being one of the LAN 4 port) then I can output the aggregated speed in the router to my pc my 2.5 GBPS LAN port to my pc which has a 2.5 WAN eth port. I know how this works, my older modem works like that. I already looked at those instruction to turn on the Link aggregation but as I said there is NO “Advanced tab” on my modems firmware (see screenshot)  for some reason. Also, yes I did check that both cables are same spec both are Cat 5e. The system I had set up is no different from what I had before which worked perfectly fine with my older modem but I had to replace the modem because it burned out and this modem claimed to support link aggregation and as it also shows in the instructions you provided me for a SB8200. Did they remove that with model 3?? If so, I am taking it back to the store. So, to reiterate, what “LAN Aggregation” in a modem does is give the spill over speed to the 2nd cable then the router combines both of those speeds to go over 1 gbps. But alas I absolutely do not see any Advanced tab in the firmware software to turn this feature on.
 

We understand that you are unable to view the “Advanced Option on the GUI Page when trying to connect “Link Aggregation.”

Please check the steps below for the Link Aggregation:

• Ensure the speed plan is revised from 1.4gbps to 800 mbps as your ISP(Xfinity) supports only 800 mbps speed plan. 
• To setup the Link aggregation need to reach your ISP(Xfinity) to assign a 2nd IP Address for the second port of the sb8200.
• Check if the Router is having the Wan Link Aggregation option.