I'm a Federal employee stuck at the GS13 level.

I'm a Federal employee stuck at the GS13 level. I got my first GS13 posting in 2010. Since then I've switched agencies three times - each time I'm promised there's room to grow, but it becomes obvious after the first year that 14s are almost impossible to get. At one point I dropped back to a 12 for 3 years, only to be told that if I wanted to get up to a 13 (again!) I'd need another 2 years at least. I have another 17 years until I'm ready to retire, and I can't stand the idea of being at the same level that whole time. I have a masters, several certifications, and 20 years of experience. Any suggestions for making that leap?