Share 'Problem Room on North Side of House'

I have a north facing bedroom on the "hit list" with 3 exterior walls and a cathedral ceiling. The room also has 30 or so sq ft of North glass. Room is 12x14 and I've already bumped the supply duct from a 6" to and 8". This helped a lot but hasn't entirely fixed the room being colder/hotter than the rest of the house.