Ron has UVerse and an extender and it slows to a crawl when he streams. Leo suspects that it's his modem that's causing the problem. It's likely an out of date modem that's slowing the network traffic down. Rebooting could help. A better Wi-Fi router could help too. Routers do wear out over time. Leo recommends the NetGear Orbi. He can set up the AT&T router to work in bridge mode and then use the new router to route the traffic. It'll be a lot better.
The chatroom suggested checking out this community page at dell.com. There seems to be an ongoing issue with some of Dell's Wi-Fi cards. This one is called the "Killer."