This invention relates to high performance RIM (reaction injection molded) poly(urethane)urea elastomers, and to a process for their production. These elastomers comprise the reaction product of an allophanate-modified diphenylmethane diisocyanate prepolymer having an NCO group content of about 5 to about 30%, with an isocyanate-reactive component comprising a high molecular weight amine-terminated polyether polyol, an aromatic diamine chain extender, and, optionally, a chain extender or crosslinker selected from the group consisting of aliphatic amine terminated polyether polyols and aliphatic hydroxyl terminated polyether polyols, optionally, in the presence of an internal mold release agent, a surfactant and a filler.