best extender for a gateway bwg320-505 that can be purchased and work with both 2.4 and 5

As mentioned above a mesh system would be a good route to go.

If you don't mind the mesh system being on a different IP range then you could bypass having to setup passthrough.

Once plugged in via ethernet to your BG320 - during installation you will be offered the choice for the mesh system to setup a network in the 10.0.0 range.

This is the way I have had mine setup for years through many different Orbi devices and it works perfectly. Whole house coverage at 100% speed using one Orbi router and 2 Orbi Satellites. 

Hello @dgl340,

We understand the gravity of having elite connectivity and are more than happy to assist you!

Let's make up for the invested time and work on a fix.

Please let us know the model of your extender as they vary?

Also, please visit our website to have a better understanding on which extender is compatible with bwg320-505 and also feel free to manage your networks in ⁠Smart Home Manager

Reach out to us if further assistance is needed.
We'll be happy to help!

Irene, AT&T Community Forum Specialist

@dgl340  You'd probably be best off to setup a mesh WiFi system with the Netgear and not use just an extender. You'd have to place your gateway in pass through mode and let the Netgear router handle all of the heavy lifting and WiFi. Or, you place your 2.4GHz devices on the Guest Network, with or without its own SSID/password and point them there.

@ATTHelp 

Read the post. They don’t have an Att extender. 

thanks for the help I will give this a try when I get a chance again