Here's another good source I've seen from the user lart2150 on reddit posted on the T-Mo subreddit: https://coverage.lart2150.com/# They use the T-Mo map and scan it to take all the info you can see in specific spots and show it nationwide. It shows pretty clear holes in the Madison market, it's definitely not great. Meanwhile back up here towards the cities I think it's probably one of their better markets.
There's quite a bit of B71 only in Northern WI, but it seems based on the TM MVNO map where you can see what LTE bands are available in a spot, B71 deployment has definitely stalled. Madison and Milwaukee are not good markets for TM, I know largely because spectrum availability is so low. Sprint isn't great in WI, but TM is even worse, especially rural. I hope they have a commitment to make it better.
The map I'm taking about: https://maps.t-mobile.com/pcc.html?map=mvno-noroam-34l
I hope TM is also committed to combining their B2 and Sprint B25 ASAP.