The difference, as it has to be, has been the curve. AJ will always have the same fastball. Decent velocity, decent movement, mediocre location. It's the curve that abandoned him last year, and has been pretty good through three innings today.
EDIT: And yeah, Tex looks locked in so far. Really like the two handed follow through, which he started towards the end of last year (and is now used by every Yankee LHH except Cano).