Zestar Issue

I talked with the nursery and they said that they thought the dieback is from how they are stored after were dug. They suggested that I cut the central stem back to where there is no dieback. I cut the trees back yesterday and it was heartbreaking. What were 6' trees are now a 3 foot something tree. In addition I was told to either create a new central leader, or to cut all of the side branches back below the cutback central leader so that the central leader is still dominant. For those trees that were tall enough and had short enough limbs I just trimmed back the side branches, but there were several that had very vigorous upright limbs which allowed me to choose one to be the replacement leader. The nursery said that in a couple of years I'll never know the difference.  I hope so, because when I walked the orchard today, the little trees mixed in with the tall ones really stand out.