New MB8600, unable to lock upstream channels

The upstream power is too high / almost out of spec on channel #4. And there is a 12 dB difference between the lowest and the highest frequency channels. There should only be a 3-4 dB difference.  That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, latency problems, and the un-bonding of channels. There is a line / connection impairment somewhere.

In an effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1000 MHz, bi-directional, and no gold colored garbage from Radio Shack, Home Depot, Target, etc. Splitters should be swapped with known to be good / new ones to test.

Also check the coax cable for any damage such as cuts, nicks, abrasions, kinks, sharp bends, etc.

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two-way splitter connected directly off of the drop from the street / pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

Good luck with it !

I am currently running 1 splitter (brand new Antronix CMC2002H-A), but I did test with 0 splitters with the line coming out of the dirt, up through the wall, and to my modem. Same inability to lock in the upstream channels.

My previous modem did not have this issue, so that's why I'm wondering if this might be a hardware issue. Or perhaps because I'm trying to move more data than previously is why I'm seeing an issue now.

Data consumption has nothing to do with the signal stat values. And it's 99% likely to be a line issue rather than a modem hardware malfunction.

If there is nothing more that can be done to improve the connection quality, then you'll need a tech out to investigate as stated. 

Bear in mind that if the premises facing techs can not find or fix a problem at your home, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem would seem to lie beyond your home in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home. And if the problem is found to be on their side of the demarcation point, there will not be any charge.

Good luck !