Engine braking. It is a useful weapon in the arsenal of driving big lumber trucks downhill. It's very useful when just exploring those out of the way areas on the maps. Sometimes the truck will want to slide down a steep incline, wheels locked up with the brakes, out of control. Selecting low 1 allows the truck to descend the hill nice and slowly, and you can still steer (important!). However, this only appears to work when going forwards. Selecting low reverse seems to allow the truck to freewheel backwards thus causing much panic and frantic mashing of the xbox One controller!
Please can this be passed on to the devs for examination and a possible update?