Answer
Gimelstob's highest singles ranking was achieved in 1999, when he reached a career-high of 63rd in the world. This was a significant accomplishment for Gimelstob, as it represented the pinnacle of his singles career. He was a talented and consistent player, but he never quite managed to break into the top 50. Nevertheless, his highest singles ranking of 63rd is a testament to his skill and dedication to the sport.