Slow speeds after switch to own modem

I recently switched modems from xfinity gateway to an Arris s34 and have been getting horrible speeds since the switch (40-50mbs down, 30-40mbs up). I pay for the gigabyte internet and had no problems before the switch. I have cat6 cord plugged into the 2.5 gb port on modem, running on cat6 to a 1 gigabyte router port. I spend a good amount of time yesterday on chat having the new modem set up as the active one and was told a signal was sent to make the speeds faster. At this point it was late so I decided to wait until morning to check. Nothing changed as far as speeds go. I tried restarting the modem hoping that would help. Ive read things saying this modem might need a "special code" to force the boot file to work, but who knows if that is true. Is there anyone who knows something about this that can help or look at? Please let me know. I need something more than what the first level associates are doing in the chat. Thanks!