I build up to 100% Fury and hit Meta, my Fury drops to 20% in about 2 seconds and then slows to the 6 Fury/second until I return to caster form. Is there a game mechanic that I'm missing? Is it just a junk skill at less than level cap? Does 100% on the bar not equal 1000 Fury? Just seems like a waste if I only get 3 demonic slash before losing form. Where am I screwing up?
It sounds a little like you are still using soul fire while in meta form... you should only be keeping up dots and using shadow bolt. Save all procs for caster form.