Power steering worked fine before

Originally my power steering did not go out. I got my car back from the dealer after getting my transmission replaced. When I got it back the mounting bolt on my power steering pump was cut off inside of the pump. We were unable to extract the bolt to re mount the pump- so. We replaced the pump.
Since I replaced my fully functioning pump my power steering will not work unless I get my rpm's up above 1500, as well as the awful noise. We then replaced the pump again and re flushed the system still not working, now I have replaced my pump a third time as well as the rack and pinion. And it is still not working. What has gone wrong? My power steering worked perfectly, and once again the only reason I replaced the pump was because we could not mount it properly and my belts kept bouncing off and snapping. Anyone have any ideas? I have used the correct fluid. The shop I had do it the last time instead of doing it myself says there are no clogs or leaks since the rack was replaced. The fluid is full, the pressure sensor has been replaced every time with the pump I work at O'reillys and not a single mechanic I run into is able to suggest anything.