My son went through the same thing.  Back then our endo told us it didn’t matter when we administered the first dose of Cortef and we could get our labs any time of the day.  We thought we were getting sound medical advice as we were see the department head at Columbus Childrens hospital.  We transferrred to a different endo at OSU that came highly recommended and the hiss 17OHP went throught he roof.  At one point believe it or not the doctor told me that my son couldn’t absorb the Cortef because we were giving it to him with milk!!!  He has always been a on the heavy side.  I tried to not make an issue of it, but it bothered him. 

I know you said you tried the Circadian rthym dosing.  We know doctor at Cincinnati Childrens and our doctor has us dose at 4:30am and get early morning labs.  This has made a world of difference in my son.  By changing the dosing schedule, his Cortef dosage was cut from 35mg daily to 17 1/2mg daily.  He is growing and losing a little bit of weight.  He looks like a totally different kid.  I hope you find out how to best help your child, I know it is extremely frustrating.