New generation of torque converter automatic transmissions (ATs) include a large number of forward gears for improved fuel economy and vehicle performance. In order to realize a mass- and packaging-efficient ATs, designers are turning to complex gearbox structures that may be characterized by prominent inertia cross-coupling. The inertia coupling is manifested in establishing additional torque transfer paths, which may have a significant influence on the AT shift dynamics. This paper aims to analyse and quantify the influence of inertia coupling on AT shift dynamics. It first outlines a model of advanced 10-speed AT dynamics. Next, quantitative indices related to inertia coupling effects are introduced and used in simulation-based analysis of influence of inertia coupling for the case of single-transition shifts. The simulations are conducted for a wide range of shifts, shift scenarios, and values of an inertia coupling weighting factor. The obtained simulation results and the corresponding shift performance indices are found to be consistent with introduced inertia coupling indices.