CM1000 slow speeds on xfinity gigabit

[Nidrews]

I've been having an issue for almost 2 months now with comcast on gigabit. I have a cm1000 (actually I bought a second to test and same issue) where I am only getting about 350-400 down on a gigabit plan. 

I can post signals but everything seems within spec, the bootfile shows I'm getting gigabit, my PC is set up for gigabit (it is the same issue on all devices) and comcast has come out three times now with techs and found no issues and customer support is totally at a loss to why I'm getting slow speeds (and honestly so am I, barring it being an issue with the router just not playing nice with comcast). 

I've seen lots of other people have these issues and I'm trying to see if anybody knew of any fixes or if I should just give up and get a different brand modem. 

[FURRYe38]

What are you speeds at the modem with a wired PC connected directly to the modem?

What is the mfr and model# of our wifi router connected to the CM modem? 

[Nidrews]

The 350-400 down is when it's directly modem into pc. If I use a router it barely drops speed (like 10mbps slower but not enough to matter when the modem is 600-650 mbps off the mark)

[FURRYe38]

Please post a copy and paste capture of the modems connection status page.

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. 
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...