This is something thats happened twice on me so far. When i am in tow/haul mode going down a hill and the truck downshifts while im slowing down to make a turn, the power steering seems to quit and almost made me go off the road. Both times the cooling fan was on as in i could really hear it whirl as the rpms went up when it downshifted. What could this be? An issue with the pump or gearbox? It hasn't happened to me before when the fan wasn't activated.