I have a 98 Ranger 4x4 4.0 V6 and was wondering what type of power steering fluid I should use...Have been getting conflicting views online. Manual says Mercon ATF...Some are saying Ford quit doing Mercon ATF and has gone to Mercon V ATF...Can I use stuff labeled as "power steering fluuid" at the auto store? Should I not use ATF fluid at all? Can I use anything that would help reduce the whining noise? What is the best to use after I flush the old out? Any help would be greatly appreciated.

At the time the vehicle was made Ford called for Mercon ATF in the power steering unit. They have since stopped making Mercon.
Use Mercon V where Mercon was previously called for. I would suggest and personally run Motorcraft Mercon V.

As for your whine, you likely have air in your system. Ford power steering pumps are a bit loud regardless. If you want motorcraft you will have to go to the dealership. If you dont want to bother with that valvoline and castrol make two mercon v specific fluids.
Its not going to cause system failure but i would not reccomend running valvoline Max Life or a universal type power steering fluid. It is likely you wont be able to tell the difference between running mercon v or "multi vehicle stuff", i just prefer motorcraft mercon v for the same price.

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'00 Ranger, supercab, flareside, 2wd, 3.0, auto, 3.73 open, Bilstein 4600s, 31x10.5x15 BFGs, 15x8 procomp 152s

Thank you very much for your response...I found Valvoline Mercon V ATF at the auto store and put that in...I didn't see Motorcraft, otherwise I would have used that...Had a little bit of shaking initially, but I assume there was still air in the system. I will keep driving it and hope the air all escapes, otherwise maybe drain and try the Motorcraft? Are there any additives you would recommend to reduce the noise?

If your steering wheel shakes and shutters when turning you have air in the lines. Im sure youve read a how to but lock the steering column left to right with wheels off ground. The rest of it will escape out eventually. Motorcraft Mercon V is only sold at ford dealerships. I dont think its going to make a noticeable difference in noise level over the valvoline fluid. They do sell additives to reduce noise. To me theyre not worth the money but you can decide if you want to try it. ChrisFix tried one here

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'00 Ranger, supercab, flareside, 2wd, 3.0, auto, 3.73 open, Bilstein 4600s, 31x10.5x15 BFGs, 15x8 procomp 152s