Gigabit Internet not working properly - Modem Issue?

I recently upgraded my service to gigabit speed. But, when I go to swap out the modem (Motorola MB8600), I can only get internet on my ethernet connected pc. It will not work on my wireless router or any other ethernet ports on my gigabit lynksis switcher. I've tried  the Arris SBG8200, and Netgear CM1200, same issue. Xfinity sent a tech, and my signal is good, no issues. My current modem is Arris SBG6400, and everything works great, but I'm only getting 250 mbps (a fraction of what I'm paying for). I was wondering if anyone had any insight on this, it just doesn't make any sense to me. Below is an explanation of how my home network is setup.

Xfinity Coax main feed into Arris SBG6400 modem, which feeds ethernet to my linksys gigabit switch. The switch feeds 10 ethernet cables (cat6) througout different rooms in my house. My wifi router is connected to one of said ethernet lines which broadcasts a great signal. 

Any help is greatly appreciated!