Aftermarket lifted packs have a larger arch and take more to flatten them out. Stock packs are the worst to use longer shackles on. If you look at your stock leaf spring and shackle setup, you will probably notice the stock pack is nearly if not already flat. Look at the shackle in relation to this. As the leaf pack flattens out, the shackle pushes back toward the rear bumper. Longer shackle means longer arch, means easier for leaf pack to stretch out and flatten or even invert. Did that make sense?
When talking a budget boost or building up lift off of stock leaf springs, blocks are the worst thing you can do, due the the taller fulcrum they become thus causing severe axle wrap. Shackles are not as bad as shackles, but they still cause premature sag for the reason I mentioned above. AAL's come in short and long. Short just suck...period. Longer AAL's help build a stronger pack but are often made to lift a tiring leaf pack on their own so they have a high spring rate causing a stiff and uncomfortable ride. So, it seems you can't win for losing when it comes to a budget boost. If only someone had done their homework and made a kit that used AAL's that matched the spring rate of the stock packs and used several of these AAL's to build up the stock spring pack the way they should have come from the factory. :wink wink: