Ihave a 2006 F150, STX. I have replaced the steering rack, power steering pump and all of the hoses. I later found out the problem was the steering shaft. I replaced that as well and now the pump stops working intermittently. It usually goes out when I exit the interstate or when I slow down from a constant highway speed. Yesterday it quit all together. This morning it was fine until I got about a mile from home. Any ideas?