diff --git a/src/e3sm_quickview/app.py b/src/e3sm_quickview/app.py
index 6b63d46..334fa30 100644
--- a/src/e3sm_quickview/app.py
+++ b/src/e3sm_quickview/app.py
@@ -562,10 +562,12 @@ async def data_loading_open(self, simulation, connectivity):
                 # Initialize dynamic index variables for each dimension
                 for dim_name in available_tracks:
                     index_var = f"{dim_name}_idx"
-                    if "time" in index_var:
-                        self.state[index_var] = 50
-                    else:
-                        self.state[index_var] = 0
+                    default_idx = 50 if "time" in index_var else 0
+                    # Clamp to the dimension: an index past the end is rejected
+                    # by the reader, and most files have far fewer than 50 steps.
+                    self.state[index_var] = min(
+                        default_idx, self.source.dimensions[dim_name].size - 1
+                    )
                     self.state.change(index_var)(
                         partial(self._on_slicing_change, dim_name, index_var)
                     )
diff --git a/src/e3sm_quickview/plugins/eam_projection.py b/src/e3sm_quickview/plugins/eam_projection.py
index a6fc9b8..e282dd8 100644
--- a/src/e3sm_quickview/plugins/eam_projection.py
+++ b/src/e3sm_quickview/plugins/eam_projection.py
@@ -133,40 +133,6 @@ def ProcessPoint(point, radius):
     return [x, y, z]
 
 
-# Slice plans keyed on the PedigreeIds array identity. Pedigree permutations
-# from vtkTableBasedClipDataSet are long-run-monotonic (typically runs of
-# thousands of +1-stepped indices), so we can replace fancy indexing with a
-# list of slice copies and reduce the per-tick cost substantially.
-_pedigree_slice_plan_cache = {}
-
-
-def _get_pedigree_slice_plan(pedigree_vtk):
-    """Return (starts, ends, pid_np) for the pedigree permutation.
-
-    The plan represents pedigree as a sequence of runs where each run i maps
-    output[starts[i]:ends[i]] ← input[pid_np[starts[i]]:pid_np[starts[i]]+len].
-    Cached by (id, MTime) of the pedigree VTK array — vtk_to_numpy returns
-    a fresh ndarray each call, so keying on ndarray identity would miss.
-    """
-    key = (id(pedigree_vtk), pedigree_vtk.GetMTime())
-    entry = _pedigree_slice_plan_cache.get(key)
-    if entry is not None:
-        return entry
-
-    pid_np = numpy_support.vtk_to_numpy(pedigree_vtk)
-    diff = np.diff(pid_np.astype(np.int64, copy=False))
-    breaks = np.flatnonzero(diff != 1)
-    starts = np.empty(len(breaks) + 1, dtype=np.int64)
-    starts[0] = 0
-    starts[1:] = breaks + 1
-    ends = np.empty_like(starts)
-    ends[:-1] = starts[1:]
-    ends[-1] = len(pid_np)
-    entry = (starts, ends, pid_np)
-    _pedigree_slice_plan_cache[key] = entry
-    return entry
-
-
 def add_cell_arrays(inData, outData, cached_output):
     """
     Adds arrays not modified in inData to outData.
@@ -175,10 +141,11 @@ def add_cell_arrays(inData, outData, cached_output):
     is different than the number of values in the arrays already processed
     through the pipeline.
 
-    The indexed copy is done in-place into a pre-allocated output buffer
-    using a cached slice plan over the pedigree permutation — roughly 2x
-    faster than fancy numpy indexing for the clip-induced permutations we
-    see here.
+    A single fancy-index gather does this. An earlier version walked the
+    permutation as a list of monotonic run slices, assuming the runs were
+    thousands of entries long. Measured against the permutations this pipeline
+    actually produces — mean run 55-110 — that loop is 8-16x *slower* than one
+    numpy gather, because the per-run Python overhead dominates.
     """
     pedigreeIds = cached_output.cell_data["PedigreeIds"]
     if pedigreeIds is None:
@@ -186,8 +153,7 @@ def add_cell_arrays(inData, outData, cached_output):
         return
 
     pedigree_vtk = cached_output.GetCellData().GetArray("PedigreeIds")
-    with _perf.timed("add_cell_arrays.slice_plan"):
-        starts, ends, pid_np = _get_pedigree_slice_plan(pedigree_vtk)
+    pid_np = numpy_support.vtk_to_numpy(pedigree_vtk)
 
     cached_cell_data = cached_output.GetCellData()
     in_cell_data = inData.GetCellData()
@@ -214,9 +180,7 @@ def add_cell_arrays(inData, outData, cached_output):
 
                 in_np = numpy_support.vtk_to_numpy(in_array)
                 out_np = numpy_support.vtk_to_numpy(out_array)
-                for s, e in zip(starts, ends):
-                    src_off = int(pid_np[s])
-                    out_np[s:e] = in_np[src_off : src_off + (e - s)]
+                out_np[...] = in_np[pid_np]
                 out_array.Modified()
 
 
diff --git a/src/e3sm_quickview/plugins/eam_reader.py b/src/e3sm_quickview/plugins/eam_reader.py
index 8ea4791..5646fdf 100644
--- a/src/e3sm_quickview/plugins/eam_reader.py
+++ b/src/e3sm_quickview/plugins/eam_reader.py
@@ -665,7 +665,15 @@ def SetSlicing(self, slice_str):
 
                 if invalid_slices:
                     print_error(f"Invalid slice indices: {', '.join(invalid_slices)}")
-                else:
+
+                # Mark modified whenever a *valid* slice changed, even if some
+                # other dimension in the same request was out of range. The
+                # valid values have already been stored, so skipping Modified()
+                # would leave the reader's state ahead of its output -- and
+                # because the caller resends the whole slicing dict every time,
+                # one stale out-of-range index would otherwise suppress every
+                # later change.
+                if self._changed_dims:
                     self.Modified()
 
             except (json.JSONDecodeError, ValueError) as e: