I suspect he is throwing the belt at high rpm because the "wrap" around the power steering pump is not enough, and the space between the two remaining pullies is too long, once you eliminate the trip the belt takes around the water pump. In belt speak, its a long way from the crank pulley to the power steering pulley, and then once you get there you are loosing almost 1/2 the amount of space the belt is riding around that PS pump pulley. The PS pump probably has a pretty big load on it, and then you are going either to the AC pump (another high drag belt driven device) or you traveling all the long free span to the alt. The belt doesn't stand much of a chance. There is too much space between the high draw PS pump and the crank and too much space from the PS pump to the high draw AC or Alt. That space is allowing the belt to flex enough to jump the small ridge that keeps it on the pullies. Once the belt climbs the outer ridge, the tensioner will relieve enough pressure to allow the belt to continue to walk off the pulley, once that belt gets past 1/2 the width of the pulley, its gone, and the tensioner is helping it leave. .

You either need to go back to the V belt two belt system with one belt driving the PS pump and the other driving the AC & alt, or the Alt and an idler/tensioner. Or you need to add an idler to replace the water pump (close to the location of the water pump) with the serpentine belt system.