Need real tech support for 5g download problems

Are you on the Nokia router or T-Mobile's newer router offering the Arcadyan router. If you are on the Arcadyan then having proper reporting is not there so it would be near impossible to determine much about the cellular connections. If you are on the Nokia router at least it would provide some metrics for the primary and secondary cellular signals. You can determine the 4G LTE and 5G NR cellular signals and also see the signal parametric values with the Nokia router at least. 

If you are using the newer Arcadyan router getting information from T-Mobile support about the channels and the towers is pretty much the only way to know more. The generic LED bars on the routers are of limited value so without knowing how strong and clean the signaling is it is hard to provide much in the way of suggestions. From the behavior you have reported it appears there is most likely work being done on the tower equipment or it is poorly managed. Since you have only ben a T-Mobile subscriber for a couple of weeks I would assume you have the Arcadyan router. Not much data can be obtained from that router so providing substantial answers is probably not going to be possible. If you can find out more about the tower and the signaling you might be able to make some headway but it will be a challenge and very frustrating if they are working on the tower.