While I never fall back to my pre-transition voice, I notice that if I am relaxed, around friends, drunk, tired or exhausted, Iwill use a voice that is really low. It takes much more conscious effort to get it up in those contexts. If I am around new people or working or doing a lot, I just also add quite a bit of pitch level to my voice. I would like the low voice to go away just as my male voice went away, but I dont manage it yet. It comes back after 15 years still. I think thats not like that for all and as i said its not my "old voice" its some sort of in-between voice that just is most comfortable.