I used to work for Cox back in the day, and often times the majority of internet related issues were actually within the residence itself. Either old cabeling, splitters going bad in the attic, or in the rare case, modems going bad.

Something to consider : The more splitters you have, the more degradation of the signal. Some older homes have single 4 or even 5 way splitters that just murder your signal strength. Consider peaking up there and replacing multi way splitters with 1 or 2 way splits.

This is for the more nerdy, but you can log into your modern via ip in your browser, and it will tell you your db signal strength thus not needing to buy special equipment. If you really want to, you can unscrew the connection going directly to the outside of your house to your modern, login, and check the connection there. If the signal is good, the problem is in your house.

You can also hire an electrician, or arc stream I think their name is, and have them do all that work for you.

Good luck