I'm having the hardest time doing M turns quickly, especially M2s. Most things I see progress on, slow as it is, but with those turns I'm like a grandpa. I silently think to myself "M, M" and go about one turn per second.
I'm gradually getting used to M turns, sounds like your brain/hands are pausing with dread when you see you need to execute an M. As much as executing the M turn I do a small re-grip that must be accurate so as not to foul the path of the middle layer with other fingers. Over time this re-grip has become more natural, reducing my apprehension and as a result my turns are getting a little faster. As I'm discovering, learning to cube demands patients, it often feels like progress is non existent, but it's there.