RE: Barbarian - My group doesn't roll for HP. In fact, I felt that the "average" roll per die type disproportionately punished the classes with higher dice types. I raised HP/level to Max die roll minus two, plus con mod. (1d6 =4, 1d8=6, 1d10=8, 1d12=10)
Perhaps consider a flat +1-2 hp/level to...