This study presents a comparative experimental investigation of two key flow unsteadiness phenomena in an overexpanded thrust-optimized parabolic (TOP) rocket nozzle: the transition from Free Shock Separation (FSS) to Restricted Shock Separation (RSS) and the onset of the End Effect Regime (EER). Using a combination of high-speed Schlieren imaging, oil film visualization, and synchronized wall pressure measurements, the study explores the unsteady dynamics of flow separation and reattachment at varying Nozzle Pressure Ratios (NPR). Higher NPR visualization of cap shock is also showed and presented. A new truncated TOP nozzle was designed and tested in a cold-flow nozzle test rig at Delft University of Technology.