My 2 1/2 year old salt wasting son, has always been slow growing.  He was diagnosed at the age of 12 days.  So he has been on medications since.  He only weighs about 27lbs and is wearing size 12-18 months.  But all blood tests have always come back good.  So I don't know if it has anything to do with the CAH.  He actually went almost a year without growing at all, then all of a sudden he grew.  Not a lot but enough to stop worrying the doctors.  Is your child on the growth chart?  If so has it always been about the same?  My doctor's have told me as long as he stays within his normal range on the chart and does not fall off, then it is ok.  Hope this helps.