Took me almost two weeks of daily practice before I lost the gag reflex. Apparently, it doesn't come back with time. Some thirty years later I surprised the endoscopy staff when I insisted that I not be given any anesthetic for my upper endoscopy. It went all the way into my stomach with no gagging.
Wow are you sure? Ive been practising deepthroating and I still gag. But you are right, I don't gag as much if I concentrate but then I lose all pleasure.