the AALs are $58. They are little thick highly arched, generic springs. I have a set. They were the only thing available at the time. They really do add a good amount of lift to the truck. But I'm not exactly sure what they do in terms of flex. they may actually counteract the regular springs in the same way a load leaf would.
Calmini has a set of Add a Leafs, for $150, which replaces the load leaf and allows the ENTIRE springpack to flex, not just the area around the AALs. Not sure if anyone has installed these by themselves, but they are definitely worth investigating. could be the difference between a new set of springs (as the AALs may cause your original springs to kink if you flex too much. Not saying it will happen, but it's a possibility.
Matt