The SB8200 won’t impact wireless speeds. 

when you’re speeds drop, test a hardwired pc/laptop that supports gigabit speeds. See what you hit. 

If you’re getting full speeds wired, then the issue is the router. 

I was originally leaning towards the router too but when the same issue has happened to 3 different routers im having trouble thinking they all have the same bad builds

Ethernet to laptop has proven to be strong with each router. It's just WiFi from router that has the consistent problem 

Hello Kyt

                  SB8200 is just a cable modem so we need to test the modem only on direct connection without router. In this case we would suggest you to monitor the modem internet on direct connection hardwired for 24hrs and if still the intermittent issue persist you can try resetting modem without coax cable for 30secs then check it again. You can also check the cable signal level to confirm whether your modem getting proper signal from the internet service provider or not by following the steps mentioned on the link below.

                  http://arris.force.com/consumers/articles/General_FAQs/SB8200-Cable-Signal-Levels

   Let us know if this helps.

It can also be Wi-Fi connection problem. I would try to place the Wi-Fi router away from other electronics (cable modems, TV).  If the Wi-Fi devices are further away, make sure they have clear line of sight, connect to 2.4 GHz (might need to manually set 2.4 GHz 1, 6, or 11.  Channel that is least congested), or might need to add Wi-Fi extenders.  If the Wi-Fi devices are closer, connect to 5 GHz for faster speed. 

Rule of thumb, 2.4 GHz covers greater distance but at lower speed than 5 GHz.  5 GHz provides faster speed on shorter distance than 2.4 GHz.