Weigh me down

What do you do when you are sooo good at your job, but can’t move in any planned career path direction because you are sooo good at your job?
I have continually increased and diversified my function by asking for more and more responsibilities. This garners attention from my supervisors (for supposed promotion) but at the same time, they find that me totally irreplaceable for all the functions I perform so well, that, in effect, my success has pegged me into an immovable spot. [Who could replace me? You’re so great at your job, they say!] What hinders my climb on the ladder of success?–the weight of a solid gold ball & chain, I’d say.