Full configuration of DHCP and other network services

The metrics seem to suggest to me you are not receiving any 5G frequency. It is so low it can't even register the 5G. That explains the speeds you get as they are primarily due to the 4G LTE signal. I have seen my upload push up to 60 MBs when on the B66 LTE signal. 

Clearly it is in a bad spot for receiving 5G. You should get onto cell mapper.net and look for 5G T-Mobile cells in the area. That is the main issue I have with the T-Mobile gateway is that placement is so critical and the antennas are all contained and there is no quick attachment for external antennas for locations where the external antenna is needed. 

Overall though the service here is good. Some users with the Sagemcon gateway have had issues with them starting to reboot frequently after a week or so of operation and found the problem repeated. Not all but some so it is not without some trials to get things happy. Some of the gateways don't do well with heat so placement due to potential over heating is also another factor to contend with.

iTinkeralot (great handle), thanks for all the information and an explanation of the metrics. As I said before, I am a bit surprised at just how good the gateway performs. We live in S. Florida in a 2200 sf house with hurricane impact windows. The gateway itself is relegated to our entertainment center where it has access to Ethernet. My project over the next couple of days is to see if converting Apple TV and a few other devices to wireless would allow me to untether it from Ethernet and experiment with the gateway in different areas of the house. I also have access to the attic. I once put an old Linksys router up there for wireless coverage and it worked great! My phone does get 5G in the house, but apparently it's not a strong enough signal for the gateway.

We don't have many choices for ISPs in this area. It's either Xfinity or AT&T. Xfinity has very good bandwidth (800-1Gb) but expensive. In addition, every 12 months I have to play the game of "what will you charge me this year." Add to that the inevitable outages with Xfinity and AT&T and you'll understand what pushed me to try the T-Mobile gateway.

We're a two-person household with plenty of devices. As an ex-IT guy, I too love to tinker with technology. We have a few computers, iPads, iPhones and Apple watches, Amazon Echo devices in multiple locations and smart switches and smart plugs throughout the house. The two TVs are set up for streaming with Apple TV. Even the garage door has a Nexx opener!  According to the gateway, it is connected to 45 devices.

While the performance of the T-Mobile gateway is obviously slower than Xfinity, it surprised me with just how well it serves out needs. The gateway's wireless is as good as the TP-Link router we were using, which is the reason I chose not to put it into AP mode.

I'm going to give it another week before I make my final decision as to whether to return the gateway to T-Mobile or keep it and dump Xfinity. If I had to make the decision today, I'd keep the gateway.

Here are a couple screen snaps of the metrics for the gateway. Not ideal per your analysis, but still giving me very good performance. (That 1-bar is 5G) Thanks for all your insight and expertise. It is greatly appreciated!

Just to give you an idea about the cellular metrics. I get three bars on both primary and secondary signals but since it is an n41 5G NR signal on the secondary my downloads can be 200-300 MBs download and the uploads with the B66 LTE frequency are usually around 28-54 MBs so it is plenty of bandwidth for our needs. Every location and cell is a bit difference for the delivery so results vary quite a bit even when the metrics look good or excellent.

You can test with Speedtest.net or say speed.cloudflare.com or fast.com or others and sort of get some good feedback from different tools. I like the cloud flare tool as the test seems pretty comprehensive. 

You can use the T-Mobile home internet mobile application to see the cellular metrics and if you experiment a bit more with the placement maybe you can get an additional bit of signal strength. The LED bars on the front of the gateway are just a general reference. If you want to know more you need to look at the cellular metrics. I can post a chart I have that explains the values. With my gateway I focused upon improving the secondary signal which is always the 5G NR where you will get the download traffic. The 4G LTE can drop a little and it will only impact uploads for the most part. The key to getting it to have better performance is to improve the signal quality RSRQ and SINR, signal to noise ratio. The RSRP, radio signal receive power is good to know but a clean quality signal will perform better. A strong signal with lots of noise and poor quality will still not perform well. 

The gateways usually perform better close to a window and higher up. The key is to find a good location where there are not obstructions between the gateway and the cellular source if possible. Keep in mind you might find a location that seems odd that it reports a better set of metrics but it could be that there is a signal reflection. The cellular signals can bounce off buildings and still reach places it might not otherwise. If you have metal screens avoid being behind those. Avoid appliances and reduce the wall surfaces as much as possible. Putting the gateway on a long extension cord and taking it for a walkabout the house is a good way to fine tune the location. 

The T-Mobile gateways do have WI-FI 6 technology and they seem to do quite well. There are not many knobs to turn but if you don't understand all the tech then that works. The only clients that can fully take advantage of the WI-FI 6 capability are those with the same newer wireless adapters. Prior generation adapters will only do what they can do. I use the T-Mobile gateway here without any additional router and I get good wireless coverage in our 2 story 3300 sq ft home. There are a few weak spots but they are not that important to cover anyway.

When it comes to boosters they currently only make the 3G/4G LTE boosters and not the 5G with MIMO technology. If you can find one it will be expensive. A decent cellular signal booster can run $400-$600 dollars and they are not worth the cost in my opinion as they are not really made with the broadband cellular gateways in mind. For cell phones they can be helpful. If you have 3 bars that is actually not bad. Try and see if you can improve the location of the gateway first.

Chart to understand the cellular metrics:

Thank you both for you answers. For the time being, I've decided to completely disconnect the TP-Link router and only use the KVD21 5G Gateway. I am surprised at how good the wireless is from the device, as it certainly mimics the coverage I was getting from the TP-Link.

I use a couple network devices that really require Ethernet, like my Silicon Dust Homerun Tuner which I use with Plex. There is no wireless option on the Homerun tuner. I've also decided to keep my Apple TV 4K connected with Ethernet. I used both ports on the back of the KVD21 5G Gateway. One goes directly to the ATV 4K and the other to a Netgear 5-port 1 GB switch where I can use Ethernet as I see fit.

I was a bit disappointed that I can only get 3 bars with 4G on the gateway, but that still gives me over 50 mbs, more than enough for a 2-person household with no gamers. It's less expensive than Xfinity and doesn't suffer from the outages that Xfinity seems to constantly have in my area.

Has anyone tried a booster antenna for 5G? Do they work? Are they worth the investment? 

At present there are no settings other than Wifi and login. Furthermore, those basic settings are now only available via the mobile app as there is no web Ui for the KVD21. You can still add your external router and enable DHCP like normal but you will have two NAT layers. While there is nothing wrong with that some applications do not work well with "double NAT". You can always try it and if you experience issues, your only option would be to switch your external router to Access Point mode which uses the TMO router's DHCP.