Constant Lag/Buffering Issues

I've had DTV Stream for about six months now, accessed on multiple TV's through Apple TV modules, and for the most part no issues up until recently.

Over the last month, there's been near constant issues with some of the channels with respect to lag/buffering. First it started with some live sports, where it would be a bit stuttered. Then it got worse. On some channels, it was more of a real lag and the broadcast audio would end up 30-60 seconds ahead of the video. Then it started on the non-sports channels as well. It doesn't seem to be set channels either. It's been all over the place in terms of what channels it affects, time of day (watch tv often late at night when the network has minimal traffic), and frequency. Sometimes it corrects itself after a few minutes, Sometimes (often) it lasts for a very long period until I ultimately turn it off or try to reboot the app/Apple TV. When I've done the latter and gone back to the channel having the issue, it's fine for a few minutes before the issue almost always starts again. 

I have AT&T Fiber, which is pretty reliable and fast. Whenever it happens, I've been running SpeedTest's and getting results in the 300-400mbps range, and in some cases 800mbps+, all of which is more than sufficient for streaming. Some of the Apple TV's that are having the issue are connected via Wifi, others are hardwired directly into a wall ethernet jack.

I should also mention that this doesn't happen on ANY other service, even ones with live sports like the ESPN, MLB & NFL apps. I've also followed all the generic tips on the DTV website (reboot the device, delete/re-install the app, reboot modem, etc.). All of these tips are generally useless if your network and/or device(s) aren't the issue, as mine aren't here.

When I called into DTV and explained this, the only suggestion the representative could offer me is to reboot the modem - again. Very frustrating that DTV has no way to support their product and can't fathom the idea that spotty streaming could at all be the result of a deficiency in their service, especially when so many people have complained about this. Any help would be appreciated. I'd like to try and resolve this issue and keep the service, but ultimately I'm not going to stick with a company with a spotty service and lousy support.