Personally I find that the AAL is a better option for me. I wanted better load support since I feel the rear suspension is too light for such a heavy vehicle. I don't like shining my headlights to the top of every car I'm behind just cause I hit the gas pedal.

With the AAL's, The rear susp. is stiffer, but not rigid. I have better support for heavy loads in the cab or when I'm towing. I may not get crazy amounts of articulation, but IMO you're gonna be more limited by the wheel wells than the suspension. Also it creates arc in the leaves and uses more leaves than the stock setup for a more progressive rate of spring compression.

Shackles only create lift and may give more droop, AAL's provide function. Also, they won't squeak if you install them correctly, not to mention improperly maintained shackles can squeak too. Poor arguement.