Chris I have this same problem that will hopefully be fixed this week. I took it to the dealer for the third time complaining about it and they ordered the parts to fix it, should be done on Thursday. I have a 2004. There have been several post about the power steering shudder. It is a common problem and there is a TSB on it. It happens exactly as you described while stopped or a very low speed. I notice it most whenever driving slowly around a parking lot and even more while backing from a parking space.
I am a bit concerned however because everything I have read on here says the fix is to replace the pump but they are not going to replace the pump but rather a couple other component of the steering system I cant recall now what they said they were but they did show me paperworkt hey had that told them that is what they should do to fix it. Anyone here think this sounds right?
Do a search for the other post and the TSB I'm betting that is the problem.