So I'm a mechanic and new to this forum because I'm really stuck. A customer brought in his 2005 Ford Mustang V6 with complaints on having no power steering. At idle, there's absolutely no PS. But when you rev up the engine a bit it comes back. Anytime the RPMs get above about 2k the power steering is fine, as well with actually driving its fine. I've flushed the system and replaced the pump. I also replaced the reservoir because the screen inside was ripped and there was heavy sludge buildup on the screen. When I first looked at it I noticed there was just generic clearish PS fluid in it. So I flushed it with Mercon V. I also vacuum bled the system multiple times. I've tried the 'Seafoam Trans Tune" as well as the "Lucas Trans/PS Additive." And still nothing. The ball joints look fine. His tie rods were shot so I replaced those too. I just don't want to charge him for a new rack and pinion if there's a chance it could be something else. Sorry about the long post but I'm desperate. I was going to replace the lines first just in case they were clogged with the sludge that got in from the reservoir. ANY info will be greatly appreciated. Thank You!!