Recently upgraded to gig speed interent from 200 mbps. Internet was performing very well (to the plan) and nearly reaching 200 on every device at all times. Within an hour of upgrading, internet speeds dropped to on avg 100 mbps. Upon investigation, my previous netgear router/modem combo device did not support gig speed but still supported 800+. So, I purchased a new modem and new router to better support gig speed and faster (should I need it in the future).
Upon installation, spoke with xfinity support to ensure device is configured properly on their end. Was told, "you are all set up and you should see your new plan speed within an hour or so". About a week and half later, 2 phone calls, 2 chats, and about 7 hours spent on the phone/chat still coming in around 100mbps. Ticket reference number CR913340245, never received the 24 hour call back.
First, you didn't even post any of the previous or new equipment makes and model numbers ?
O/k, start with this;
Try calling 1-800-comcast and ask a rep to completely remove the modem from your account and to "re-provision" it from scratch. Also ask them to confirm that the provisioning and account data in their database is correct and complete and that the correct configuration / bootfile for your subscribed to speed tier is being pushed to the modem.
O/k well that shows you where the bottleneck lies. Your modem is getting supplied your speeds from them.