A phenomenological pom-pom model, which utilizes linear stress relaxation data as an input, is proposed for simulating the detailed retraction behavior of a full pom-pom chain as well as the associated nonlinear stress relaxation in single-step shear flows. Specifically, the initial, Rouse-like arm and/or backbone retraction as well as the long-time, renormalized (dumbbell-like) backbone retraction is simulated at one time, and a possible coupling between linear orientation relaxation and nonlinear stretch relaxation due to diffusive or convective constraint release is self-consistently accounted for. The model’s predictions are systematically tested against nonlinear stress relaxation data on three nearly monodisperse pom-pom melts, including two six-arm pom-pom polybutadienes (PPBDs) and an H-shaped polyisoprene (PPI). The model can describe the present data reasonably well by incorporating a previously proposed effect of drag–strain coupling. Accounting further for the effect of constraint release, due primarily to arm diffusive motion and its coupling with a known polydispersity in arm molecular weight distribution, appreciably broadens the predicted nonlinear stress relaxation and substantially improves the results of theory/data comparisons. The significance of the current findings is discussed.