Extremely Slow Speeds at night and Weekends, please Help!

In the past 2 weeks my Internet download speeds have gotten extremely slow at night (after 7pm CST) and on weekends as well. I currently have the preferred tier of service. At night the download speed drops to 8-12Mbps.

During the day, and after 11:30pm or so, like magic the speed goes back to ~50Mbps. The upload speed seems to constantly hang around 20Mbps.

Here's what I've tried so far:

I've tried plugging the modem directly into the wall bypassing all power strips/surge protectors, there are no splitters in the cable run, it is plugged directly into the wall and there are no other cable outlets in the house, I've reseated the coax connections, Reseated the Ethernet connections, and cycled power on the modem.

The modem I am using is one supplied by Cox, it is a Cisco DPC3825 Docsis 3.0 Modem / Gateway.

I have tried testing speeds from speedtest.net and Cox's own speed test (from the correct market) on Cox.com, and other speed test sites, the results are pretty much the same..

As of this posting my speeds are 13 Mbps Down / 23 Mbps up @ 10:30

The modem signal levels an other info show as following:

Any help would be greatly appreciated!

Thanks!