Cox slowing down Internet during the day

Las Vegas 89123.

Cox UPGRADED our internet two weeks ago.

Now my 1 Gig service that only reached 300Meg when up to 600Meg BUT!

BUT now it's speed is maybe 600 Meg in the Morning and slows all day to around 30 Meg by evening.

This is now happing EVERYDAY.

I called COX and got the ' Is your equipment more that two years old question." 

Motorola 8200 DOCIS 3.1and AC-5300 router.

600Meg in morning and 30 Meg at night, NOT my equipment problem.

Anyone else seen this NEW problem.

Funny I had at least a STEADY 300 Meg before the HUGE NEIGHBORHOOD UPGRADE!

I'm paying for 1 Gig service and now getting 30 Meg service.