Who is your ISP?

[stevech]

Motorola SB5100 cable modem. Works fine.
Address 192.168.100.1 yields displays from modem. One is signal conditions. Watching this over time will tell you if things go marginal due to a flakey coax or system problems on their side. Also compare to neighbors'.

My good norms are
downstream signal strength -8 dBm plus or minus 6. More negative is bad.
upstream signal 40dBm plus or minus 5. More positive is bad. This is the one to watch closely. If it gets into the 50s, you've got a flakey coax somewhere, or they do. Their cable system head-end controls the upstream signal strength - it asks for a stronger signal if their end is a weak signal. The downstream is uncontrolled- just affected by your coax/splitters and their offered signal.

The upstream is low frequency. The downstream is high. So a break or poor connection in the center conductor of the coax somewhere will affect the upstream more than the downstream.

There should be one 2-way splitter between your cable modem and the main coax entering the house. And that should be ahead of any whole-house amps you have.

A well trained (few are) tech from the cable co. should know all this and check it all. Even if they have to be pushed and prodded to crawl in the attic or under the house. Replace coax while there, just in case.