fyi, 5GHz is not about more bandwidth, but it's just another frequency band used to accommodate more wireless users in the same physical area. The actual data throughput depends much more on regular radio transmission issues like line of sight, frequency, interfering signals, etc.
As people noted here, 5GHz tends to bounce off of solid materials, especially as they get more metallic in nature.
Vs 2.4GHz which penetrates more through solid surfaces, hence why it's preferred for things outside the home like cameras, temp gauges, etc that have to link to routers inside the home. If there was a wireless network at 800-900MHz (0.8GHz), then you'd have even better range. Remember the old 800 MHz cordless phone kits? They had excellent range, but then they phased those out for 2.4 and higher frequency which had much less range.
One quick way to diagnose your WiFi equipped Traeger is turn it on, go to Settings, make sure it is not paired with a previous WiFi router (like mine was... it was just stuck searching for the previous owners setup), then notice the Traeger 4 digit ID, and go into your phone (sitting next to the Traeger) and go into WiFi settings and look for a WiFi service that is like "Traeger-1234" for example. If you see that, then the Traeger Wifi system is ready to be paired up with your app.
If you do not see this, and the Settings show that it is not paired with a router already, then probably the antenna or something in the controller is messed up. If the Traeger is paired with a router already, then there is a setting choice called 'Forget Network' iirc and after you do that, you should be able to find it on your phone's WiFi list of 'routers' you can connect to.
In fact go ahead and connect your phone to the Traeger if you can, using the UUID (Settings) as the Traeger WiFi password.
You won't have internet access of course through the Traeger, but you'll know that at least your app can connect to it. And it should make the app pairing go smoother, too.