71GTO,  the other large trees that I have in large pots are in a 4-1-1 or 4-1-1-1 mix and don't seem to be a problem.  I can stick my finger down into the mix and get that cold feeling that indicates moisture.  The branches look good, they seem flexible, and the buds look good.
  It is just this one large tree that I didn't repot when I got it...it was already in a nice big pot, but the potting medium seems problematic.
I think what contributed to the problem is that a lot of my trees really didn't want to go into dormancy this Fall.  You may have had the same problem.  I withheld water a bit to coax them  to go to sleep.  In the case of this particular tree, I may have started my own problem right there.  The soil may have dried out too much originally, and then when I subsequently watered them, the water didn't really soak into the medium.
Jim