Poor Ping (>400), Download (<2 Mbps) and Upload (0.25 Mbps) with my Inspiron 13 7353 2-in-1. When not connected, the ATT Modem gives great Ping (<30), Download (>7 Mbps) and Upload (1.7 Mbps) with other devices!

I have a 2 year old Inspiron 13 7353 2-in-1.  Recently the network speeds have been very erratic. Updated the drivers, bios to the latest.  The settings  were verified as recommended in Video on Troubleshooting Wireless Network Issues in Windows 10.  The network speed is still very slow and unreliable. When the laptop is disconnected, other devices (cellphones, desktops, lenovo laptop) showed the network is good speeds as expected (ping <30, 7.5 Mbps Upload and 1.5 Mbps) with my ATT internet. After spending several hours to fix this problem ATT tech narrowed down the issue to the Dell Laptop. I hope this is not a hardware problem - any help will be greatly appreciated.