Rebuilt WDM3A locos are just as powerful as the WDM3D locos. Only difference would be the starting TE (30.4t for 3A, 38.2t for 3D due to the presence of High Adhesion Bogies in 3D). Also, axle load of a WDM3D is marginally higher (19.5 tons in place of 18.8 tons).
But yes, both loco classes are certified to operate at 120 km/h only.