Poor dowload speed

I have Blast 300 service and my interent doesn't run above 90 mbps (wired & wireless) - I used to get up to and sometimes over 300.  I'm using my own Arris SB6183 modem coupled with a Netgear Orbi AC3000 and a Netgear 24 port switch.  Comcast has been out once and put in a new box outside but that did not solve this problem.  The only thing that is different this year vs last is that I have new cat6a wiring and a total of 16 devices now connected including thermostates (4), Alexa devices (2), iphones (3), laptops (3), printer, Harmony hub, NAS, TV (last year it was about half this).  Most of the time we are only actively using two laptops as there are only two of us in the house.  I've reset the modem but am at a loss as to what else it could be.  Thanks