Can not maintain my speed of 600 mps

I have an XB6 from Comcast as well as a netgear 4 port gigabit switch since there are only 2 wired ports on the XB6 Gateway and I have 3 wired devices, 2 computer systems and a Brother Printer.

 

When I restart my gateway and run the xFi speed test I get 700-710 mps d/l. A couple of hours later I get 290-310 mps d/l speed. It doesn't matter what time of day or night, same thing happens.

 

My system has Intel i5 with a SSD main drive, purchased the latest NIC card as the system is 5 yrs old on the hope the built-in NIC on the motherboard was the problem.  It wasn't, still 290-310 speeds.

I have had Comcast Techs as well as the Sr Field Engineer and all connections and lines to the pole are in spec.

 

My wife works from home, so calling comcast tech support durring her work hours is a no go.  This is the 3rd XB6 I have had.  Running Win10 with all the latest updates and Windows Security.

 

I am enclosing a tracert route below:

tracert www.comcast.net

Tracing route to e7010.dscg.akamaiedge.net [2600:1407:5800:8a3::1b62]
over a maximum of 30 hops:

1 1 ms <1 ms <1 ms 2601:7c0:c100:23e0:a656:ccff:fe8a:e0d1
2 7 ms 7 ms 7 ms 2001:558:40a1:4::1
3 7 ms 7 ms 7 ms 2001:558:352:fffa::1
4 9 ms 8 ms 7 ms 2001:558:350:55::2
5 12 ms 8 ms 7 ms ae-3-ar04.huntsville.al.hunts.comcast.net [2001:558:350:5c::1]
6 13 ms 14 ms 13 ms ae-100-ar01.b0atlanta.ga.atlanta.comcast.net [2001:558:140:15::1]
7 * 15 ms * be-33031-cs03.56marietta.ga.ibone.comcast.net [2001:558:3:2d2::1]
8 15 ms 14 ms 13 ms be-1312-cr12.56marietta.ga.ibone.comcast.net [2001:558:3:b6::2]
9 32 ms 32 ms 35 ms be-301-cr11.chicago.il.ibone.comcast.net [2001:558:3:168::2]
10 32 ms 32 ms 32 ms be-1211-cs02.chicago.il.ibone.comcast.net [2001:558:3:105::1]
11 33 ms 32 ms 33 ms be-1212-cr12.chicago.il.ibone.comcast.net [2001:558:3:109::2]
12 * * * Request timed out.
13 35 ms * * be-1113-cs01.350ecermak.il.ibone.comcast.net [2001:558:3:c8::1]
14 31 ms 32 ms 33 ms be-2103-pe03.350ecermak.il.ibone.comcast.net [2001:558:3:144::2]
15 34 ms 35 ms 32 ms 2001:559:0:2e::22
16 33 ms 34 ms 32 ms g2600-1407-5800-08a3-0000-0000-0000-1b62.deploy.static.akamaitechnologies.com [2600:1407:5800:8a3::1b62]

Trace complete.

 

Any thoughts or things I can try?  The speeds are the same on my wife's comupter.

 

Thanks in advance,

Cadman01