Home Internet, slow speed

There are cellular signal boosters but a bueno one comes with a bit of investment. There are plenty of 4G LTE boosters but currently there do not appear to be good offerings for 5G NR boosters that also can handle the MIMO. The related technology for 5G does not appear to yet be available. The main thing to keep in mind is that a cellular booster/repeater can only do so much. If the signal source is too weak to be functional the booster will not be able to provide a significant improvement. 

There are also antenna solutions available that help improve cellular signal reception but again you have to have something stable and reasonable to work with to achieve the performance you need/want. Under reasonable conditions external antenna solutions can make a huge difference as they can improve the signal so signal quality is better and unwanted RF noise is prevented. 

If you are in an urban location where T-Mobile is expanding the 5G network there will be a higher density of towers and cells so it could be they are still "working out the bugs". I am not a T-Mobile employee. I am just stating what I believe are plausible reasons for the condition. If there is truly congestion then the current 5G roll out in the area is probably NOT complete nor engineered properly at some point. The antennas may not be phased properly OR it could be you receive a signal in the location that is reflected and the reflection causes some distortion to the cellular signal. 

It would be good to know what frequency the signal your gateway receives. If it is the n41 or n71 and the cellular metrics also could help explain more about the actual reception you have. If you have either of the two newer gateways you will need to use the T-Mobile home internet mobile application to manage the gateway. There is more reporting in the mobile application which makes it the ONLY option actually. The web connection to the Arcadyan or the newer gateway they offer is pretty useless. Having the information may not do much for you in terms of "fixing" the problems but you will be better informed of what you are up against. T-Mobile support may be telling you this or that but it is difficult or near impossible to know for sure the truth of the matter. Only the engineers working on the local equipment really have some knowledge of what is taking place and some good idea how long it will take to get things operating as they should. 

Each and every location is a bit different so results for uses can vary considerably. Your proximity to a tower or towers is always a factor. If you are close to the signal source and the signal is strong, clean and stable with a good clear exposure it often works quite well. If there are trees, hills, buildings etc… plus the distance to the tower is greater; results even without congestion can be sketchy at times. 

My best guess, given I have insufficient data nor significant historical reference, is that there is work still being done in the area and the cells are still being worked on. When work was done here the behavior I observed was that things could be highly unpredictable for a week or so as improvements were performed. I am in a rural area so it is not as complicated as in an urban area where cell towers are in a more densely populated area and more cellular signals from different carriers. Sure the signals should not overlap but delivery for individual carriers does take time and work to optimize the delivery. 

If you have the PCI for the 4G and 5G signals you can possibly leverage CellMapper.net to locate the tower and have a good idea of how far away it is and in what direction. Some of the newer 5G cells are not in the CellMapper database but the 4G primary signal often is. The more information you have/know the better you can decide what you need to do. Push them to provide more clarity on the current cell deployment in the area. If they are doing upgrades and expanding the number of cells that could account for the unpredictable behavior. Of course it could be in part due to the prioritization chocking the delivery to a point that it is absurd and near useless. High speed internet delivery is not defined in single digits. Even low double digits is not acceptable in 2022.