Definitely if you want to read out your boost you'll have to get a boost gauge as the AP won't have that parameter.
If I was you I would call COBB the day you order...tell them where you are in the states and have them ship out a new Boost Hose Line specifically for your state and elevation.
Don't waste your time buying the ap and going thru the hassle of realizing the boost isn't right and call cobb afterwards...just get it done up front then you won't be another guy iritated that his boost isn't hitting the right levels