I'm using a GM pump hooked up to a Chrysler rack & pinion, fortunately the truck was on jack stands for testing. I started the engine and everything seemed fine until I moved the wheel to the left a little it immediately shot to the right so fast it nearly broke my thumb. Two things were wrong, first the pump put out to much pressure and the rebuilt rack had been plumbed backwards making left right and right left.
The pressure issue was solved with an adjustable power steering valve. It works by sending excess pressure to the return line, this design does not depend on a spring to regulate pressure making it simple and safe, of course I also switched the lines on the rack. I'd read where GM used more pressure than Ford or Chrysler that's why I tested it on stands before driving it. Here's a link to the valve - http://www.speedwaymotors.com/Adjust...lve,14895.html
So far everything works great, I've done multiple quick left/right steering test at up to about 45 mph, I have a few more things to do before going any faster.
I had a bad experience with a chopped '30 Model A I built a few years ago, drove great at 40 mph but the first time I tried highway speeds all hell broke loose, I wanted to go left and the car wanted to go right. This was caused by suspension induced steering, it was solved with a Panard Bar, I've been driving it for over 5 years with no more steering problems.