i did my grille and lower valence with it and love it! sucks about the heat issue, how many coats did you do? its relatively a new issue on this website so i would try searching google to find a quick answer.
Thats why the parts stores carry special paint for wheels. Wheels can exposed to lots of elements and the brake heat can be hard on the finish of even regular paint. I would remove and redo with a paint meant for the task.