This work, builds on the authors' recent CFD research on high speed gearbox windage loss [1-4]. There, 3D steady and unsteady, single phase simulations of spur gears were presented. Those studies served to elucidate some of the physics of windage losses, validate the methods and models employed against available experimental data, and explore design alternatives to mitigate windage loss. With this validated capability in hand, we have recently studied computationally two critical design relevant components of high speed gearbox aerodynamics: 1) The role of shrouds, widely used in rotorcraft transmission systems for windage loss mitigation, and 2) the role of lubricant transport, i.e., the multiphase flow resident in real gearboxes. Research findings and attendant recommended design guidance are reported in this paper.