Here is the PS/Hydroboost Flush procedure
Here is the repost. I cleaned it up a bit to make it easier to read and follow....
I can't remember if I jacked mine up or not, it'll probably be easier on the pump if you do. Anyways, if you do jack the front of the truck up to take some pressure off the tires...don't go too high or you won't be able to reach to refill the resevoir.
Under the hood on the driver's side next to the firewall up high in the corner there is a rubber return line w/ a pinch-clamp holding it on. It's real obvious and the only one there. I removed the clamp and hose, then I attached a piece of clear 3/8" tubing 6.5ft long onto the fitting using a small hose clamp. I ran the other end to a catch pan on the floor. Make sure that you put something on the end of the hose in the catch-pan so the hose will stay in the pan when the old fluid starts pumping out. (w/clear tubing it's easier to see when the fluid turns clean)
Start the truck, in park, slowly depress the brake pedal as far as you can and hold it there. Then turn your steering wheel clockwise 1/4 turn, back to center, then 1/4 turn counter clockwise then back to center. Slowly release the brake pedal and then re-apply brake, and turn steering wheel again. Continue this procedure until you hear the pump make noise (mine took 3 iterations). Stop! immediately and turn off the truck.
Fill the power steering reservoir with fresh power steering fluid (I used NAPA brand which is actually valvoline $12.99 a gallon). Then repeat this procedure until you see clear fluid coming from the hose.
Mine took a little over 3/4 of a gallon. Probably more than I needed but I wanted to get as much of the old stuff out as I could, and like I said, the old fluid was BLACK! Also, make sure there is enough new fluid left over to refill the power steering pump when you're done.
Then, remove the clear hose and re-attach the rubber return line.
IMPORTANT: After you refill the final time, start the truck and move the wheel back and forth, then recheck fluid level, add if needed. All done.
This is really a simple thing to do, so much so, that you'll probably want to do it as a regular maintenance item...say every year or two.
