Dislocation velocities in silicon in the experimental range of temperature and stress are studied a priori by combining a mechanistic treatment of elementary kink processes with activation energies obtained by atomistic calculations. Pronounced effects of intrinsic coupling of the dissociated partial dislocations are captured in kinetic Monte Carlo simulations, which are consistent with observed velocity variations with applied stress. As a result, the nature of "weak obstacles" to kink propagation, a long-standing postulate in previous data interpretation, is clarified. A striking new effect is predicted and offered for experimental verification when dislocation velocity shows nonmonotonic oscillatory behavior with increasing stress.