Low Downstream Channel Power

I recently moved and this is my first time using xfinity as my ISP.  Since moving, I've had very low internet speed.  Sometimes only 0.5 mbps when I'm paying for 200 mbps.  I am using an Arris SB8200 modem and an Airport Extreme router.  I did some investigating and found that my downstream channel power was too low.  It was around -35 dBmV for most of the channels and the majority were not locked.

 

After several phone calls and chats with Xfinity agents, they kept saying it was my router or my modem so they sent me an Xfi gateway to see if I still had the problem.  The speed was a little bit better but still not what it was supposed to be and the connection would randomly drop off.  On the modem's admin page, I found that it was only locked onto one downstream channel and the power was -20 dBmV.  Finally, I was able to get a technician to come out and check the line.  Turns out there was water in the service line, so he replaced it and checked the connection inside.  He said everything was fixed and my equipment should work just fine.

 

I switched back to using my Arris immediately after.  I checked the power on the channels again and while it has improved, it seems that it is still outside the acceptable range.  I am still getting inconsistent speeds.  These are my power levels after the technician came out.

Does this mean it is my modem that's the problem?  I think the xfi gateway modem uses DOCSIS 3.0 and my Arris is DOCSIS 3.1.  Would this make a difference to my speeds?