Psych is definitely a shelf where a high number of practice questions is critical. There really isn't that much material to test, honestly, so the questions focus more on the details of distinguishing one diagnosis from another in terms of time, number of symptoms, etc. I will say this can be a tricky shelf for some - I always mention a buddy of mine who was a 260+ guy across all his Step exams and who finished all of his shelf exam in about 45 minutes. He crushed every test he ever took except the psych shelf, and he did fine on it too, but it was definitely his kryptonite because of the long vignettes and importance of one detail that changed it from the obvious diagnosis to another.
The nice thing is that there aren't really that many diagnoses in the field as whole compared to other clerkships. As such, if you go through 2 different question sources in their entirety, you should be almost sure to ace this sucker.