Thanks for the answer, I personally would buy the tractor there (in Colorado) if that's where your going to need to use it, I do believe the dealers in Colorado will be very aware of the problems associated with high altitude use.
It would also be cheaper not to have to haul the tractor there from Alabama.
Going with a turbo model will lessen the issues, but a turbo in a B just isn't practical, jump up to an L then it would make more sense.
Edit: I reread your post, and you already have the tractor, maybe talk to a dealer in CO and see if they can make the adjustments for cheap enough for you.