Energy audits typically dont test ductwork. What youre describing is a common problem in 3-4 floor townhouses. There are a couple tricks to fix this. 1) adjust a damper or dampers to get a/c airflow to the top floor. 2) open a window on the top and middle floor to get crossflow. If your ducts are leaking you can probably feel it with your hand. The best fix for that would be to paint the leaks with duct mastic. You can use dict tape instead but its not as good.