I'm pretty sure that the truck's MAF sensor is able to adjust for the altitude since its primary job is to measure the volume of air that enters the engine. I know that old vehicles and the diesels sometimes have a problem with it since they dont have MAF sensors or any way to correct automatically. I do know that Bill makes adjustments to the WOT fuel based on altitude because during WOT the truck fuels based on that number instead of the sensors.
Usually 5000 ft is the limit of low to high altitude tuning. Since you hover there all the time your truck (most of the time) experiences changes of about 3000 ft. The altitude section on the order form just helps give a ball park of where to set it.
I'll see if I can get Cody to comment, he actually knows what he's talking about.
