How can I tell if a cell tower is broadcasting 5G?

ChuckC3, Depending upon the terrain the 5G can reach out and be quite functional 4-5 miles out. I receive my signals from a tower right at 5 miles North of my home. I have a distinct advantage in that I live up upon a ridge at 1450 ft elevation and the tower is a little higher plus it appears to be ~100 Ft tall tower. i can see the entire tower so it delivers a very good n71 signal even out this far. It may be those two towers have 5G on them but a cell is not covering your area. CellMapper.net is roughly 80% complete as it depends upon users uploading info to the server database. You are right with the T-Mobile solution you would receive either the n71 or the n41 band for 5G. The n41 is more commonly seen in higher density areas as it does not reach out as far as the n71. The n71 is a longer frequency so reaches out farther and penetrates a little better. If you have a 5G Apple cell phone you can put it into Field Test Mode by dialing *3001#12345#* and checking the LTE and 5G NR information. If you have an Android phone there are some cellular networking apps that you can download and use to try to find cellular metrics information and such. 

It might be worth contacting T-Mobile and asking more specific questions about coverage in your location. Maybe checking on Twitter or Facebook for the T-Force community. Reddit is of course yet another source of information. Maybe there will be 5G coverage there soon. When it is done right it is a nice solution for a good price.