There are no recalls or special policies for the steering or brakes pertaining to your concerns. I did find this bulletin for a similar concern. Also, if the hydroboost or hydraulic portion is leaking replace under warranty. Make sure it's not a leaking shock at the same time. I have seen the hydroboost units leak on these trucks.
#05-02-32-008B: EI06002 - 670 Gear Box Power Steering Pump, P/S Performance Concerns - (Jul 18, 2007)
This bulletin is being revised to add model years and models. Please discard Corporate Bulletin Number 05-02-32-008A (Section 02 -- Steering).
Some customers may comment on a lack of steering assist when stopped or during parking lot type maneuvers. A lack of steering assist could occur if the brakes are applied and turning the steering wheel with the vehicle stopped or during parking lot type maneuvers. This condition will go away or greatly improve once vehicle begins to move or is above parking lot speeds. This concern can be aggravated by worn tires, low tire air pressure, low power steering pump pressures, and tires larger than stock size.
Important: In all cases, it is recommended that the proper tire size and the maximum tire pressure is set according to the manufacturer's specification as noted on the door placard; especially for the front tires.
Power Steering Gear
Inlet O-ring Seal