I have a hard time backing up with this 2004 Chevy truck, I need it for my farm. No one knows how to fix the problem. There is no noise, it's just hard to steer.

The truck power steering doesn't work when the truck is idling below 500 RPM. This has gone on from 2004 until now and still has the same problem. I recently looked for an idle adjust and couldn't find one. This problem really surfaces when trying to back up a trailer

Ive taken the truck to the dealer many times, they have no idea how to fix the problem. I was told GM knows about it, but doesn't know how to fix it. How about changing the pully size because when you bring up engine speed the power steering works.