Slower than normal internet

A little history, In the past few years I have subscribed to the Prefered internet tier (50mbs) which speed tested at 50 to 60 mbs download and also the Premier internet tier of 100 which speed tested at 116 to 119 mbs download .  to cut cost I downgraded back to the 50 mbs service and recently noticed that my speeds were testing around 10 to 12 mbs down, so I called Cox support and they said the see no problems in the Cox network.  I then figured to resolve the slower than normal connection I would just upgrade to the 100 mbs tier again since it was only $5 a month more.  I did this and I was only getting 40 to 50 mbs speeds.  I then called Cox support again and they said everything looks good in Cox network.... of course this was testing with there support tech and rebooting my modem several times and testing with and without my router in the mix....... same result...everything good in cox network. This was using the same equipment I have been using and getting great speed test in the past (cisco 3010 docis 3 modem and netgear n900 router)

so I bit the bullet and went and bought a new docis 3 modem SB6183 with 12 downstream channels (since my cisco only had 8) and a new Netgear Nighthawk X4.... low and behold, same result the best I get is 52 mbs.  I have run this test several times to 3 different COX servers.  these are my modem numbers: