Let us assume we are talking about a tow vehicle's ability to dissipate the difference in potential energy of a truck/trailer combo during the descent of a downhill grade. Let us also assume that the truck is not a hybrid and does not store any energy in a battery or flywheel, and that the speed and associated kinetic energy of the truck/trailer combo (hopefully) does not increase while descending the grade. Then 100% of the potential energy difference (mass of truck/trailer combo times the difference in elevation) must be converted to heat, either through aerodynamic drag, disk and drum brake heating, or engine and transmission braking (or really long skid marks
Given the above simplified black box model, I find it hard to believe that a light duty passenger vehicle is as capable of converting that energy to heat as a purpose built truck that is designed to do just that. I believe that heavy duty brakes, transmissions, and engines brakes have less to do with total stopping power from 60 - 0 and more to do with sustaining that braking power over prolonged periods of time, as in going down long grades.
Not preaching or advising any course of action, just my thoughts on how I would approach a seemingly difficult problem, using a simplified physical analysis, to inform my selection of an appropriate tow vehicle.