My 98 k2500 with vortec 7.4l has hydroboost brakes, and at idle and just above idle rpm, it has no power assist in the steering. Even in neutral while revving the motor. Once moving and rpm increases, the power assist returns. Is this a sign of a bad pump, or weak pump, and are the power steering pumps the same for hydroboost and non- hydroboost equipped vehicles? Would fluid contamination be a possible cause of this?
It could be a sign of a weak pump. Power steering is made to assist turning the steering box while you are driving. When the tire is rolling the friction to the pavement is reduced so it will be easier to turn. It is not uncommon to have the steering to be difficult if you try to turn the steering wheel while at a complete stop with the brakes on. But, if you have no power steering assist at all I would look at the pump pressure and see what it is doing.