Hmm, off the top of my head I would the fallowing are the most likly cause:
1. The advanced DNS feature is giving you a different IP for the domain you are pinging and that IP is further away.
2. The router is giving a lower priority to ICMP packets you are using to test with.
3. There is latency some outside of your LAN that is unrelated to your new hardware.
And this is how I would test for those three possibilities:
1A. Perform a trace router. Start > Run > CMD > Tracert [insert ip or domain]. Compare with the DGL to direct to the modem. Different?
1B. Turn off Advanced DNS and see if there is any improvement.
2. Previous test should also show this. If you see the latency spike on the first two hops, then thats the router. Doesn't mean its effecting performance. Do you know how to test with TCP?
3. Again, the previous test should show this. If the spike is at the 4th or 5th hop, then its outside your controll. If its still in your ISP's network, I would say contact them, but realistically, they probably won't do anything.
Questions:
1. Do you actually see performance decreases? Do you get lag during the game? I don't just mean a ping rate, do things actually lag. IE Slow mo, time skip, game boots, etc.
2. Any problems with your phone?
3. Any problems with other high priority traffic? Stream video or music?