Given the information regarding the problem with DMZ+ mode on my AT&T Gateway, I decided to reconfigure my home network. Without going into too much detail, I reset the Gateway to remove DMZ + (standard configuration) and put my two WiFi base stations into bridge mode in a WiFi roaming configuration, moving the router responsibilities back onto the Gateway. This involved a variety of tasks through the admin pages of the devices and associated resets to bring up the network under the new configuration, as well as some minor changes to my physical cable connections.
Testing the internet speed from my computer (connected via a switch and associated Cat6 cables) now gives download speeds of 78 Mbps and 65 Mbps with two different test services. Note that these are both above the 50 Mbps limit of the Gateway when using the prior setup with my primary WiFi router DMZ + enabled. My service speed is advertised as 75 Mbps.
So this solution solves the speed limiting problem with using DMZ+ mode and allows me to utilize a much better WiFi roaming network than could be achieved with the WiFi in the Gateway.
Testing the internet speed from my computer (connected via a switch and associated Cat6 cables) now gives download speeds of 78 Mbps and 65 Mbps with two different test services. Note that these are both above the 50 Mbps limit of the Gateway when using the prior setup with my primary WiFi router DMZ + enabled. My service speed is advertised as 75 Mbps.
So this solution solves the speed limiting problem with using DMZ+ mode and allows me to utilize a much better WiFi roaming network than could be achieved with the WiFi in the Gateway.