The rutting performance of polymer-modified dense-graded and rubberized gap-graded asphalt mixes used in composite pavement was evaluated with full-scale accelerated pavement testing with the heavy vehicle simulator (HVS) and laboratory test results. The effect of asphalt layer thickness on measured surface deformation for both mix types was also investigated for recommendations for future design. In addition, the progression of the rutting failure mechanism for both mix types was evaluated with transverse cross sections measured with a laser profilometer at various HVS load repetitions. The polymer-modified dense-graded mix performed better than the rubberized gap-graded mix under both laboratory and HVS testing. The greater shear movement of the rubberized gap-graded mix under HVS loading caused larger humps, which consequently increased the maximum deformation and resulted in earlier failure. Larger aggregate size and denser gradation for the polymer-modified dense-graded mix resulted in more efficient dissipation of shear stresses and created greater permanent deformation resistance.