Hugely variable speeds

I'm having similar issues. I've been with t mobile for over 30 years, on the 5G internet plan for over a year. I'm talking home wifi. I've had download speeds of over 200 and speeds of 5. Upload speed over 30 and at other times .04.  I also have a computer directly connected to the router.  I assume they are doing work on the tower or something.  I've tried to troubleshoot to see if it varies with weekday vs weekend, or time of day. There is some variance based on highg demand times but nothing radical. I've tried rebooting everything,  router, phone computer. If using the phone for testing I'm standing next to the router. And, as mentioned,  the computer is hard wired with ethernet cable.  

I live in the Great Bridge area of Chesapeake near Oscar Smith high school.