Internet service extremely unstable

Is that a direct connection to your modem, or are the any splitters involved?  You're running high on signal power.  I don't know if your error counters are actually working or enabled in your firmware or not.  You've got something acting like a notch filter, so that suggests a component of some kind hanging off your coax that isn't helping you out. 

A lot of splitters are also signal attenuators that reduce power by 4-6 dBmV typically.  You could bypass the splitter, but then you'll see the signal power go even higher, but try bypassing it for a test if there is one and take a look at the signal table again.  See if that frequency dependent power increase on high and low frequency goes away (your ODFM channel is the highest there at 850Mhz, and high at low end at 483Mhz).  They should all be pretty close at all frequencies.  

In an ideal case, you'd see 0 dBmV for signal power.  That would be dead center in a range of -7dBmV to +7dBmV (negative values are OK).  Signal will also vary during the day by a couple of dBmV sometimes, so headroom to allow for that is desirable. 

It might be the problem or not, but it's always good to start out by trying to get the signals more in spec first before trying anything else.  Cheaper than a service call for a test -- would be removing the splitter and buying a attenuator, or just trying an attenuator if this is a direct connection.  If you search on amazon, they are about $10-15 if you search for "PPC FPA6-54 in-line Forward Path Attenuator 6dB 75 Ohams for DOCSIS....".   You might be able to find one cheaper somewhere else.  You can screw it right to the back of your modem.