AT&T U-verse internet is unreliable/spotty with wired connection

We've had AT&T U-verse + Direct TV for maybe a little over two weeks now and so far the internet has been randomly dropping and is just unreliable for what seems to be no reason at all. The RG model is a 5268AC with a built in router. Normally there is someone always on the wireless side of things, but for me specifically I have a wired connection to the modem itself via the power lines and I still get random ping spikes and connection drops that last for nearly ten seconds. With our previous internet provider I had none of these issues. I had a wired connection via power lines and usually the wifi was always being used by someone else but it still ran fine.

I'm curious to see if the router inside the modem is causing issues for whatever reason. With our previous setup, the router was wired to the modem, not a modem-router combo. Of course this is just a guess, I really have no idea why the internet is so spotty, especially with a wired connection.

I'd appreciate if anyone has any tips or tricks that I could do or check to see what the issue is. If the issue is the service itself then I'd like to know for a fact rather than just guess what the problem could be.

Thank's in advance.