My 01 has the same issue, really quite bad when I am trying to back in a trailer. I took mine to the dealer and they said that it was normal if you had underinflated stock tires or even oversized tires. The tech told me that the power steering system at idle was only designed to overcome the resistance that a stock size tire creates againt the pavement. So any oversized, aggressive or underinflated tire will cause poor powersteering at idle. I have 315 Allterrains on my truck and apparently that is plenty to cause the problem,
Sounds like some really crappy engineering to me since you really need the powersteering the most when you are still or moving very slowly.
I would really like to find an aftermarket product to help, since it really sucks when you are in a tight spot with a trailer.