[GCncsuHD]

^Exactly what he said. For each inch in difference of "effective" length of the shackle, you will get 1/2 that amount in lift/lower. So for the 2" drop, the shackle is 4" longer than the stock shackle. Use the top set of holes for the most drop, usually the different holes are used to correct a little lean from side to side.

Also make sure you are only tightening the bolts on the shackles after you have the trucks weight on the ground (or jack the axle up to mimic the trucks weight on the ground if you need to leave it on jackstands to get under it). Too many times have I seen/heard people complain they didn't get the full amount of drop or a rough ride after they tightened the shackles down with the suspension drooped, which effectively preloads the suspension at that height.