Likely one of the accessory pulleys or an idler/tensioner. Or both. Does it do it with A/C on and off? A/C pumps can whine as well; usually when they are low on freon. So can alternators. So can water pumps. How do you know for sure it's not the PS pump? Could also be bearings in the water pump. Any water seepage at all? Does it go away with RPM fluctuation or change with it? Any maintenance done recently? Does the sound change when you turn the wheel? Is it the same from startup as it is when warm? Does it change with a load? i.e., idle/rev in park vs driving? Have any of the accessories ever been changed? If so, when and which one(s)? Are you able to induce a change in the sound/pitch at all? If so, how? How many miles on the truck? Did you buy it new? How much did you pay for it? When did you buy it? Does it have any mods? If so, what are they? What size tires does it have on it?
Haha... okay, a few of those were just so I could get to the proverbial 'what is this, 20 questions?' mark, but the rest are serious questions you need to answer so that anyone here can try to help you diagnose the issue(s). Do your homework!