My tmobile cell tower is overloading my router settings to make it worse

I am curious as to how you determined "they" changed the way TCP is functioning. Are you taking packet captures and doing in depth packet analysis of the sessions or what? The normal operations with TCP when there is congestion is to use a sliding window dynamically, making it smaller or larger when possible. The two hosts in the session communicate back and forth to optimize the flow based upon how much data can be received before the acknowledgement. It is a function of the TCP/IP stack operation based upon IEEE standards. The two end devices determine the window size. That is normal.

“One thing they did was change the TCP so any new connection starts out with a very slow download and then it ramps up to better speeds” (the two devices in the session)=they 

I would guess that there was some congestion and the routers and the hosts in the session were compensating with a dynamic window size to address the congestion. Analysis of the packets in a capture should provide some profile of the traffic. I am just going to make a guess you are in an urban area and not a rural location. Please correct me if I am wrong. What I have observed from community conversations that users on the n41 band in a urban area where tower density is greater tend to see more congestion due to more users and I personally think the cells are loaded heavy. I could be wrong as I have no way to know how many subscribers are loaded on a given n41 cell source but I have seen more people in urban areas complaining about congestion. I live in a rural area with n41 and my downloads can be 250-400 MBps and varies depending upon the time of day/night and load. 

The cellular signal metrics you have posted on the middle capture are pretty awesome. The RSRP, reference signal receive power for both the 4G LTE and the 5G frequencies is in the good & excellent range and the SINR is excellent as well. The RSRQ, reference signal quality for the LTE is good and the RSRQ for the 5G is excellent. 

The signal quality in all three captures is good to excellent and the SINR though down on the middle capture after the gateway was restarted is still in the excellent range. So the metrics changed but the reason appears to be maybe not what is speculated. More data is needed to reveal a better picture. IF you notice on the first and last the 4G LTE band is a B66 frequency. The middle capture reflects B71 on the 4G LTE. So, I would expect the upload traffic to be a bit lower. It is not possible to tell with just the cellular metrics for the signal power, quality, and signal to noise ratio IF the gateway acquired a lock on a different cell or not as there are NO PCI values for the specific 4G LTE signals nor the 5G signals. 

I can only speculate that there might be another tower or cells that the gateway gets a lock on and makes a transition from one cell to another on both the 4G LTE and the 5G NR frequencies. If you see the significant cellular metrics change AND the bands change look for the PCI, physical cell identifier, and see if you can locate both cell sources. Goto CellMapper.net and confirm both 4G and 5G cells. It might be that your location is between the cell sources and makes a transition in part due to the RSRP change and congestion. I am not sure how far your location is from the n41 source but 168 MBps down with n41 is not that impressive. Clearly the b71 and b66 are two different 4G LTE cells. Confirm the n41 5G cells as those will do the heavy lifting for the download traffic. A little more digging suggested.

The signal quality as you put it is not changed by someone. It is changed by environmental factors and cell fuente lock more than likely. Just like mobile handsets can jump from one cellular source to another the gateway might be making the same signal handoff or transition.