CM700 high US/UnCorrectables

Hi all,

I have been experiencing internet issues for the last 3 years at my home.
I found that my US(Upstream) power (modem transmitting data to the ISP) was intermittently maxing out (I forget the max for the SB Modem, but it was ~50dBmV) resulting in T3 and eventually T4’s multiple times/day.

I went outside and connected modem directly to the drop outside and found levels were good(US was ~40-42dBmV) and DS was good (~0dBmV +/- 1dBmV)
Ultimately, my solution was to remove the 3-way splitter and the 2-way splitter that was installed and connect drop directly to modem upstairs.
This helped for a bit.. until it didn’t.
Initially I assumed the problem was my Surfboard Modem (after blaming Spectrum/TimeWarner for a year).
So I got the CM700 Modem and Nighthawk Router. Things were good for a few weeks.
Then T3/T4’s began due to high US signals.
SNR ~40dBmV for each Channel
US rising from ~45dBmV following reboot to >50dBmV resulting in reboot.

I went outside every day to re-seat the coax connection from the drop to my line upstairs. I replaced the mating connector at one point, same thing. I eventually found a GND wire tucked into the conduit below that was never connected to the GND terminal of the splitter I removed. Without a splitter, I didn’t have a good way to terminate the GND to my line.

- Yesterday -
I verified continuity between this GND conductor and the metal conduit of my electrical power meter (DMM 2WIRE DCR ~0.5 Ohms). I went ahead and stripped about 5 inches of insulation off and wrapped this best I could to make good contact with all 3 chassis/housing terminations(drop coax, mating coax, upstairs coax) and verified DCR of <1 Ohm from each to electrical meter GND.
Due to corrosion, rain, wind, etc. I go out about every week to remove the oxidized/corroded layer off this ground wire and re-wrap around coax. I plan to install the new enclosure I ordered and terminate GND correctly per code if Spectrum doesn’t do this for me.
I even tried grounding the shield of the coax connected to my modem upstairs by cutting a 3 prong AC adapter and wrapping the GND conductor around the shield terminal at my modem and plugging this into the wall upstairs. But later figured this could just cause more problems due to differential voltage between GND upstairs VS GND at drop and removed this.

- Current Day -
After the reboot yesterday, it reset my corrected/uncorrectables. So I took a screenshot of this to reference. Today (<24 hours following reboot) each DS channel has 100 - 4,000 UnCorrectables.

- Here is my Question -
I am thinking about installing the original splitter (still in good condition physically, assuming electrically as well) and seeing if the 3.5dB attenuation will help. I will likely terminate the other 3.5dB OUT with a 75 Ohm resistor or equivalent if I still see problems. But wanted a second opinion on the situation.
Due to reasonably good SNR, should I install a drop amp? After hours of googling around, I realize this is not the favorite solution of Cable Techs.
I do not have an oscilloscope to compare signal between Drop - upstairs coax, and would rather not crawl through my damp crawl space to inspect every inch of coax line and check for additional terminations/problems.
Is there anything else I can do to ensure the problem is not caused by faulty wiring in my home? I am a Technician where I work, but have little background/experience with RF in general but would love to learn more.
Specifically regarding: Testing for/causes/potential solutions of Ingress/Egress leakage, etc. Because I have a feeling noise is the Root Cause here.
As a final note, I have no problem at all purchasing a signal generator/injector and/or oscilloscope (price within reason) or other tools to Test/verify these issues myself.

Any help/input/ideas are greatly appreciated.
If more information is needed, don’t hesitate to ask. I’ll try to upload any logs I can to assist.
Thank you,
- Robert