Re: Power steering out at park/stop
Did you hear any whining or other weird noises when turning the wheel?
Almost all of the time, a ps pump will let you know it is near failure by making a horrible screaming/screaching noise when you turn the wheel. I'd be surprised that the pump gave out without this happening.
As mentioned above, the first thing to check is fluid level, quality, and type. The 5.7 requires hydraulic fluid, not transmission fluid like most other motors.
If you have fluid in there, I would check the condition of the belt and make sure it isn't slipping on the pulley (again, this would likely make a lot of noise).
If you still can't find the culprit, it may be something with the steering rack itself, though this would be less likely.