[Sephiroth]

Here goes for an attempted explanation. What Moldova says is, of course, your only way forward.

There are a number of timers (T1 through T4). In this case, the T3 timer covers what is known as a "ranging request" sent to the CMTS (head end). After each unsuccessful attempt (i.e. no reply), the upstream power is increased until it reaches its maximum - whereupon a T3 timeout occurs.

When you are connected to the internet, then I would expect to see the upstream power level rather lower (let us know please).

To my mind, the modem is behaving properly but somewhere in the circuit on the other side of the modem, there is a problem. It starts with the coax cable needing to be properly screwed in both ends, goes on to noise anywhere on the line between your gaff and the CMTS.

So, if it's not a loose cable, an engineer it has to be and I suspect some street or cabinet work.