Loss of power steering

[onebad65c10]

Good day. I have a problem and just looking for a little input.
I have a 2005 Chevy Silverado Extended cab Short box Z-71, 4wd, 5.3, 126,xxx miles. Recently I have been having what I could only describe as loss of power steering at low speed and idle. It has been a intermittent problem. Now it seems to be getting worse. If when this happens and I give the truck a little throttle the power steering comes back. I checked the fluid level and it is fine both hot and cold. The truck does have the P/s Cooler as part of the Off road package. I really don't want to take this to a dealership and get raped saying the whole steering system has to be replaced. I have read on a couple of posts that there is a small electrical piece on the pump for the speed sensitive power steering. Just wondering if that may be it. If anyone here has had this happen to their trucks any input would be appreciated.

Thanks
Phil