My silverado lost power steering and power brakes. They still work like manual when at a dead stop or low rpm. When test driving it I realized that at 1500 rpm or above the power steering and brakes operate normally. When I slow back down they fail again.

What is your question?

My mechanic feels since the power steering pump is only a year old, it is probably the steering/brake assist unit. I assume that is the hydro boost I have seen in searching. Does this seem to be a reasonable guess? It is not leaking and the belt/tensioner/ pump pulley all seem to be fine. Any tips on swap out and bleeding if I do replace it?