cm1000v2 Xfinity speed dropped after install

[melkweg]

Hello- I am troubleshooting with Xfinity speed issues with cm1000v2, Firmware Version V7.01.01.

I am getting 30-40mbps download speed with a new CM1000v2 but paying for 600mbps. The CM1000v2 is replacing a TP-Link TC-7610. The TC-7610 is getting speeds of 200-300mbps download speeds- much higher

I am replacing the TC-7610 because it's only a DOCSIS 3.0 rated modem thinking a CM1000v2 DOCSIS 3.1 rated modem could help reach the 600mbps download speed we are paying for.

I've also tried and returned a Motorola MB8600 which also only reached 30-40mbps download speeds.

Xfinity support is not any help since this is a customer owned modem. Before I call back and ask for service appointment for them to check the coaxel to our house, is there anything in the below logs that points to something specific?

With the TC-7610 getting much faster speeds, what the heck is the issue?

logs

[melkweg]

Attached is screen of CM1000v2 logs files.

[FURRYe38]

If you tried two different modems and expeirence same problem, Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
Be sure to power OFF the modem for 1 minute them back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...

[melkweg]

Any feedback on the attached log files screen capture? Comcast will be on site today to check the line and looking for anything I can point out to the technicial. The power values for all downstream channels are negative. Is that the issue? Low signal power = only 30mbps of the 600mbps currently?

I don't know about splitters. We don't coaxle cable in the house except for thw cable modem and there's no splitter on the single cable between the modem and wall jack.

We've powered over several times and I connect one computer directly to modem ethernet with same low speed.

[FURRYe38]

Have the ISP check everything with you. Have them check with there PC connected to the modem.