may be too much cement?
Its in your mix design. Tweek it a bit more.
Here are a couple of additives that should help.
Utah has huge deposits of diatomaceous earth, try a bit of that mixed in as well
Ugh, dreaded shrink. refer to this FAQ. It applies to the vertical mixes in general, not just ad pacs. Vertical is very demanding an many many factors are involved. Post pics if you can as that can help the experts on here better diagnose.
thickness, scratchcoats, control joints, etc all come into play.