Recently Announced Internet Speed "Boost" Not Working

**UPDATE**: I finally received my replacement cable modem, an ARRIS SB6190, and am now receiving my correct Internet speed of 150 Mbps. I still have no idea why my old SB6183 was connecting to my computer and my router at only 100 Mbps, because the specs are clear that it is supposed to contain a Gigabit LAN port. In any event, with a lighter wallet and a faster connection, I sign off from this forum and thank everyone who tried to help. Good luck with your future issues! **END of UPDATE**

Well, after much experimentation, I have isolated my problem to the cable modem itself, my ARRIS SB6183. Even though it supposedly carries specs saying it has an internal Gigabit Ethernet Adapter, I cannot force it to connect to anything faster than 100 Mbps. I used 5 different Ethernet cables, 3 different computers, removed the router from the chain, and even tried disconnecting Cox's cable from the back of the modem, and it stubbornly insists on connecting to anything and everything at no more than 100 Mbps. All I can conclude is that either the specs are wrong, and that the modem does NOT contain a Gigabit Ethernet Adapter, or that it is defective, and is downgrading itself to a 100 Mbps connection to compensate for an internal malfunction. Either way, the only remaining step is to try another cable modem, which I do not have at this time. If I take that step, I will report back with an update. I might just surrender and live with it.