The slab dip and long-term coupling at the plate interface can vary both between and within subduction zones. How these variations affect the long-term subduction dynamics and mantle rheology is important for understanding plate tectonics and its evolution. This paper presents two-dimensional (2D) models that examine the surface plate velocity and dynamic weakening of the asthenosphere as a function of six values of plate interface coupling (3.1x10^20, 1x10^21, 3.1x10^21, 1x10^22, 3.1x10^22, 1.0x10^23 Pa·s) and three values of initial slab dip (30^o, 45^o, 60^o). The models use a composite viscosity in the upper mantle and were run for 2000 time-steps. The instantaneous results show subducting plate speed and dynamic weakening at the lithosphere-asthenosphere boundary (LAB) increase with decreasing inter-plate coupling, and peak for models with an initial dip of 45^o. For time-dependent models, subducting plate speed also increases with decreasing inter-plate coupling. However, models with an initial slab dip of 30^o produce the fastest subducting plate speeds over time. The thickness of the dynamically weakened LAB evolves over the course of subduction. The results indicate the subducting plate velocity is correlated not only with the imposed inter-plate coupling, but also with the dynamic weakening of the LAB region. The weaker the inter-plate coupling, the easier for the slab to descend into the mantle and dynamically weaken the asthenosphere due to the strain-rate dependent rheology. This reduced viscous resistance to slab sinking facilitates subducting plate and mantle flow over time, thus easing the subduction process of plate tectonics.