I’ve been using OpenDNS on one of my computers, it works well.
I am a former cable technician, and here is my educated guess:
Looking at those levels from your modem, I think that your modem is coming off a splitter AFTER the first splitter. This causes the levels to drop significantly, which can cause intermittent issues. The system should go like this:
Pole to house, where it gets screwed into a grounding block, usually hidden in the plastic box on the outside of your house.
From that grounding block, there should be a piece of cable going to a splitter. This, optimally, should be a two-way splitter (one input, two outputs). One of the output legs needs to have a cable going directly to the modem with NO further splitters in it. The other leg should go to another splitter or splitters, which should feed your TVs.
If there is a three-way splitter where I just described the two way splitter, make sure that the cable going to your modem is coming from the leg marked “-3.5 dB”; that is how much signal the splitter is cutting from that particular leg.
If you need to reconfigure the cables, all you’ll need is a 7/16" wrench for the coax connector and a pair of pliers to hold the splitter.