I also think hypothyroidism or Cushings Disease could be the problem.
I have found most of my own dogs to be sensitive to Evo food, but I haven't tried the Innova line which isn't quite as rich as the Evo. A grain-free food that I have found to be very well tolerated by every dog I know that has tried it is Orijen.
Roxy - Feb 2005 - 75 lb American Staffordshire Bull Terrier (adopted Jul 2011)
Peewee - Jan 2006 - 8 lb Chihuahua (adopted May 2009)
Myka - Nov 1998 to Jan 2010 - 85 lb American Pit Bull Terrier cross
Lacy - Sept 1992 to July 2003 - 18 lb Reg Shetland Sheepdog