I'm a systems admin/onsite IT for a manufacturing firm. My fluency used to be dogshit until I got a job answering phones for a helpdesk and the sink or swim environment really got me over it somehow. I hardly ever stutter now, just occasionally. I don't suggest this will solve everybody's issue of course, but I think a lot of it for me personally was just learning to not care. My first time being mocked for stuttering at that phone job and it was super heartbreaking and my boss was just like "Ok, well fuck THAT person" and he demoted them to email only support and they hated it. He just didnt give a shit. That made me realize my boss had my back and if somebody's gonna mock me, i'll just hang up on them.