The thing about radio and rom combos is that they sometimes contain updated modules that take advantage of the radio version you have.
Some users note that certain radio firmware work better with a certain rom while another rom hinders it. Less Battery life or signal.
You can stick to one rom and flash any radio you want and not notice a difference because of where you live while others will.
Radio updates don't control what bands you phone uses they simply make adjustments on how your phone uses them. So your T-Mo HTC One and my AT&T HTC One if they where to have the same ROM/Radio the difference in battery life and overall network performance depends on just that; the network.
If your having issues related to the T-Mobile network it could be any number of things. A bad rom flash, Radio firmware not at your favor, the phone itself, or just the local towers etc.
There are several radios available to install via recovery.. Try a couple and test each out for a day or so and compare the results. If not try to stick with the radio that was released with the ruu the rom was made from.