Ok folks, I'm here to bring you the 5.1 radio from the latest GPE update. I snagged it from another thread and set it up as a flashable zip. Keep in mind that radios are essentially drivers for your modem so they are platform agnostic.
Radio Lollipop 5.1 (4T.36.3218.06_10.33R.1718.01L) HTC One M7 Flashable ZIP
If you hate my radio choice, feel free to replace the radio.img with your own radio.img file and then you have your very own custom flashable radio! Now spread joy upon the land with your new radio flashing / creating abilities!
Thanks santod040 for the original radio! (Note you can dump your current modem with either ADB or Fastboot, can't remember which one off the top of my head... perhaps both work!).