BBL, Your signal looks very good to me, your SNR(37-38dB) matches mine almost and your power levels are all within spec. So I am doubting your issue lies there.
Usually when its congestion the speeds will fall, like in my case I had 4Mbps on my speedtests with the high ping at one point. »www.speedtest.net/
Run a speedtest from that site or run one of dude's linked tests or both(preferably) during the high ping times and the results here.
Well you could give them the ip of the server that is having issues, that is why I did twice and on the second time I think I got a Tier 3 person with extra stuff and she went to the right people and it got fixed fast once they were made aware of it, never to happen again.