In one of my schedules, almost half of the items have more than 80+ days of slack, on a schedule that I expect to be complete in about 4 months. This seems a lot of activities to me, and I dont think that many activities can have that much slack on a schedule that will finish in 4 months. What am I doing wrong? Does it mean they are probably missing some successor activities tied to them? By the way all my activities in the schedule have a successor, including those high slack activities.

My guess would be that the tasks with the large amount of slack are not directly driving their successors because they are not the only predecessor to the task.

Other things like constraints and deadlines also alter slack.