Kind of a stupid question but do your use the upper holes for the mount or the lower ones to get the 1 1/2" drop. I assume you can get 2" by using the upper holes & 1 1/2" by the lower ones. Also which way does the bracket face forward (open end or closed end.
The upper holes on the bracket will lower the truck slightly more than the middle holes. I installed my shackles with the open end facing the rear of the truck but the shackles appear symmetrical so I don't believe it is a major issue. Also I used the upper shackle holes. If you have a 99 lightning this will generally level out your truck's ride height and you won't have to adjust the pinion angle for the driveshaft. Later year lightnings have larger leaf springs for more load capacity which gives them a slightly taller rear end making a lower drop generally better for them.