Relativistic (>1 MeV) electron flux increases in the Earth's radiation belts are significantly underestimated by models that only include transport and loss processes, suggesting that some additional acceleration process is required. Here we use a new, three-dimensional code that includes radial diffusion and quasi-linear pitch angle and energy diffusion due to chorus waves, including cross terms, to simulate the 9 October 1990 magnetic storm. The diffusion coefficients are activity dependent, and time-dependent boundary conditions are imposed on all six boundary faces, taken from fits to CRRES Medium Electrons A electron data. Although the main phase dropout is not fully captured, the persistent phase space density peaks observed during the recovery phase are well explained, but this requires both chorus wave acceleration and radial diffusion.