OS Apps Will Not Load on My New 5G T Mobile Internet Device

If you have an Ethernet adapter you can connect to your MB Air wire it to the GW and check to see if there are software updates pending. If there are then allow the update to take place and give it another try with the wireless connection. I had a similar issue with my MB Pro and it was being difficult due to a pending update that would not complete. If you don't have an Ethernet adapter for the Air then take it where you can get it to connect. IF the issue is only with MAC centric applications I would check out the  current OS status and just make sure there is not some pending update causing a bit of mischief. 

If you can use the terminal and ping major DNS providers, and run speed tests and what not it may just be a simple update issue or getting connected to your Apple account. If it was working before using the T-Mobile GW then going to the coffee shop and confirming it works there might help.