Firestick will not connect to T-Mobile Home Internet

I have spent hours upon hours trying to find a solution to this issue. I am trying to assist my mother (remotely) in getting her Firestick Lite to work with her newly acquired TMobile Home internet (Gateway FAST 5688W). I see so much on the internet but have not found anything that seemed to have fixed the issue as of yet. The problem is the Firestick will drop out with a check internet connection message on the screen at random times. However, while I am watching the PC speeds are still amazingly fast (for her area 70mbps) at the time of a dropout from the FireStick. The gateway is about 5 feet away from the FireStick. I have created a second network for only 2.4ghz and lowered it down to WPA2 from WPA3 (all things that have addressed others issues that I read online). She was using her HOTSPOT on her Tmobile phone for the Firestick (Speeds around 3.5mbps) and never had these issues prior. I have read similar posts where the firestick would work off of a hotspot but would have similar issues with TMobile home internet, of course there were no follow-up solution's to those posts. If anyone has any other thoughts or suggestions it would be deeply appreciated. This is really becoming crazy!