QoS or other method to improve online gaming packet loss / ping with Pace 5268AC modem/router.

Hello all,

My problem is this: When I get off work in the evenings and try to use my Xbox One for online gaming, I experience extensive network issues ("lag") to the extent that the game is unplayable. It happens every night like clockwork. Very rarely does it happen in the middle of the day or after midnight, usually happens at about "netflix o'clock". At first, I was convinced that it was an issue outside my house and that it was a fact of life that all my neighbors hog up the internet of the area as we all get online at the same time. I did further research and did everything I could to remove Wifi frequency interference and this has not fixed the issue. (May I add that hard wiring is not an option as my router is on a different floor in a three story town home with 2 roommates.)

I have since become thoroughly educated on the subject and believe this issue may be due to other devices on my network such as our U-verse television boxes, a roommate's web browser on PC, or netflix, etc. using the network and queuing devices data transfers and causing packet loss. It is my understanding that web browsers and video streaming devices tend to suck up close to 100% of the network bandwidth regardless of what your ISP mbps plan is (it could be 100mbps or even 1Gig or it could be <18mbps and these devices will still queue bandwidth by hogging it all up. 

So my questions are as follows:

1) Is my understanding correct?

2) Is it possible with the AT&T 5268AC router to enable QoS and prioritize my gaming bandwidth traffic by prioritizing bandwidth by either static IP address or otherwise with this router?

3) Or if not "QoS" any other method to ensure my xbox latency / ping is as low as possible from the internal network standpoint? 

I should add that I do have quite a bit of experience logging into my gateway on this router and changing settings for wifi channels and for opening ports or putting my xbox in the DMZ, but none of this has helped my problem. Always getting less than 6-7 and commonly less than 3 or even <1 mbps on my Xbox in the evenings and my ping is always >100 ms.

Thanks in advance for your responses.

PS: I have already had an AT&T tech out to my house to replace the modem and box and run diagnostics and it did nothing for my problem. He said my network was fine and to be honest when I asked him my questions such as above he didn't know what I was talking about I don't know if he was even that technically well versed.