Do the water trick where you take a spray bottle and spray tap water onto the back side (flat) of the belt, if the noise goes away then you have a tension issue. If the noise doesn't then spray the ribbed side of the belt, if the noise goes away then you have a pulley that is misaligned. I know you did the water side but just wanted to tell you what it means when you do it so you know
you NEVER should use wd-40 or any lubricant on the belt. That is like putting tire gloss on the driving part of your tire and expecting it to have a good grip on the road. Water is the ONLY thing you should spray on the belt to isolate problems.
Since you mentioned spraying the ribbed part, spray just the flat and see if that affects it at all. Having a misaligned pulley isn't very common but can still happen and they are harder to fix sometimes than a tension issue. When you run the engine that wobble you are seeing on the PS pump and water pump should be almost non existent. My water pump has very little play, about 1/16" so its normal. My idler pulley has the same amount of play too. The water pump has 0 play on mine. What you can do that I do once in awhile regardless if there are any noises under the hood or not is to take some brake cleaner and paper towels and remove the belt and then clean every single pulley with the brake cleaner. DO NOT spray the brake cleaner on the pulleys as if you get some into the areas where the bearings and covers go it can break down the rubber covers and the grease in the ball bearings. Just spray the brake cleaner on the paper towel and wipe down the pulleys with it.
Can you see any glazing on your belts back side? Can you read the manufacturing information stamped onto the back of the belt or is it really worn out? If you look at the edge of your belt is it straight or somewhat cupped? When you experience the squeal noise has your truck been sitting awhile, has it rained since the last time it was running, are you putting the engine under load (like turning your steering wheel or loading down the alternator with a lot of electrical load)?
edit: any cracking on the belt is an immediate reason to replace the belt IMO. Don't take that chance of it snapping from age and fatigue while you are driving on the thruway or anything like that.