Should I replace just the door slab or the entire pre-hung door?

Slab-only replacement saves $80–$200 per door but only works if your existing jamb is straight, undamaged, and the new slab matches the old slab's hinge positions and dimensions exactly. If your existing jambs are 25+ years old, painted multiple times, or any door currently sticks or binds, replace the full pre-hung unit. The labor savings from skipping jamb work disappear if the new slab needs custom mortising or weatherstripping rework. On exterior doors, ALWAYS replace the pre-hung unit — weatherstripping integration is critical and rarely works on slab-only swaps.