I tried flushing the fluid, not really figuring it would fix anything, but it was cheap and easy, but it was, of course, a waste of time.
Does anyone have any info to add to this?
I wouldn't call it a waste of time replacing the PSF for once in the vehicle's life. Any fresh hydraulic fluid or other misc lubes will be nearly transparent; when the chemical becomes nontransparent, it is saturated with various contaminants, at which point the fluid intended to support the system becomes a major liability. Any and all of the various system-supporting and assembly-lubricating fluids will become compromised with age/time, heat, friction, metallurgy, moisture, foreign contaminants, and so on. All of the fluids have to be replaced BEFORE the end of service life, not at the first sign of trouble.
I've investigated the contents of 100,000 mile PSF and it's much worse than a 100,000-mile brake fluid. Just 100% saturated with black particles that is the inside lining of hoses and a cloudy slurry which makes up the super fine mixture of metals from the pump rotor and overall degradation of organic compounds. All of the power steering pump rotors I have seen are a metal-on-metal mechanism, such when a fluid loses its lubricating properties after a decade, irreversible damage begins to occur.
Had you flushed & replaced the PSF say 5 or 10-years ago, the PS system in question would still be running strong and far from a topic of concern.
Then you have these hydroboost systems with the GM trucks where people have problems with the brake performance & reliability either before or along with the steering. Some owners take immediate action and have the good fortune of saving everything with $20 in supplies & 2-hours simple labor while others continue to neglect an obvious need for service or repair with exponential consequence.
While you are replacing the steering gear, might I suggest draining & replacing all of the other systems. Transmission, differential, coolant, brakes, everything. It will save you money in the long run. Prevent any catastrophic failures & extend the life of original systems. these trucks will run forever on the original parts if driven conservatively and components serviced [completely] within the manufacturer's schedule of maintenance & inspection. Maybe you missed that boat but better late than never.