Final Update: I wanted to provide a fair and acurate picture of what turned out to be causing my constant T3/T4 timeouts & the out of range errors in the CM1000 log. Whether the recent firmware update did or didn't increase the power level for some users, I do not know. But I didn't want to leave my contribution to this thread hanging with the impression that my issues were caused by a CM1000 firmware update. In fact, the unit was just reporting the true state of the signal it was receiving, and correctly timing out when that signal degraded so low that it could not hold sync.
A while back, I had suspected that my splitters and/or the original house cabling (circa 1998) might be the cultprit. So I replaced my splitters with properly rated (supposedly) higher quality ones. Saw little if any change. I even removed extra splitter down to just one and used termination caps on unused ends.
So I called out a Comcast tech who checked and replaced the cable line coming from the street to my house. While his external signal levels were much improved, I still had intermittent issues getting a good quality signal inside. Even after purchasing all new networking gear (Netgear CM1000 and Orbi RBK53 Router & 2 Sats), I was still having issues. So I knew something was still very wrong after continuing to see frequent T3/4 timeouts and out of range warnings, which a reset would only remedy for a short time.
So I decided to connect the cable line from the street directly into my CM1000 router and observe the status and signal levels myself. Sure enough, it immediately went from reporting terrible Power and so-so SNR levels to showing much improved numbers across all 24 bonded channels:
Reported ranges using home cabling & splitters:
Power : -13.2 to -10.4 dBmV <-- BAD!
SNR : 37.5 to 39.6 dB
Reported ranges after direct cable connection:
Power : + 7.9 to +10.2 dBmV
SNR : 40.4 to 41.5 dB
So then I began testing all the various splitters I had on hand, by directly adding each, one-by-one, between the cable line from the street and my CM1000 modem:
Rating Brand Comments
1/5 IDEAL 4 way splitter Junk. Noticeable quality drop off above 700000000 Hz
2/5 Comscope (red) splitter Poor, recommended and provided by last Comcast tech
3/5 TVC 3.5db / 7db splitter Good, but not great; original equip, installed new in 1998
4/5 Using GE (square) splitter Quite good, surprising since I see posts bashing these
5/5 Extreme (square) splitter Very good, numbers were nearly the same as direct connect
So in the end, I discovered that my poor signal quality issues were primarily due to the splitters I was using (and by mistakenly trusting a Comcast tech to provide a good quality splitter which was crap). Even worse, I had been using two splitters in series--one at the main manifold in the attic, then another in the family room splitting a line between the cable TV box and the CM1000 modem--which further degrading the signal.
My "semi-scientific" testing also showed that just the original house cabling itself was dropping the signal a noticeable amount as well. I'm not sure if it was the run-length causing it or the quality of the cable used from 1998. Regardless, I now have the info I need to change out the inside components to effect a much better signal. So the CM1000 modem and its recent firmware were not a contributing factor in my particular case.
