Have you/they(endos)  thought of hypoglycimia (sp?).  If his levels are OK it seems that maybe something additional is going on.  Does he only respond to additional Cortef or if you give him gatorade with sugar in it?  Have you thought about trying DEX which is longer acting?

I am sorry you are having such a hard time-  keep pressing the doctors,  I truly believe the squeeky wheel does get more attention in these situtations.

 

Best of luck