Bought my 95 5.0 a few months ago
When I bought it it had a slight chirp didn't think anything of it thought it was an easy fix
The slight chirp progressed into an aggressive squeal
Finally changed the belt assuming it was just a little stretched and the it went away
2 days after the chirp came back still slight but now it's getting a lot worse again
Thought it might be the tensioner so I tried adding some tension to the belt while the truck was running with a wrench and nothing Changed So Idt Its a Bad Tensioner
Just bought some belt dressing to see if that would help and it immediately made it 100% worse
Anybody else have this problem I'm assuming it's a pulley at this point but Irdk

 

Belt dressing makes it tremendously worse. And I've inspected every pulley on this truck and it still squeals. It chirps very slightly most days but if its wet or abnormally cold it gets LOUD. I've found that a dap of dielectric grease on both sides of the belt shuts it up for 2-3 days. I keep a giant tube in my door pocket now

 

Look at the pulleys from the side and check for one of them running out of line. In my case it was tensioner running out of line with the smog pump and the alternator. Try it with the belt on first, I could see my belt exiting the pump and running towards the front of the truck.
I originally thought it was an alternator bearing because it was screeching so bad. I went to a trusted auto electric shop, with the engine running, the tech dumped a cup of water on the belt and it was quiet for a few seconds so he said it was a belt issue.
I emailed Dayco because I had put a new belt on and thought it was defective. I told them about the cup of water ect. In me return email they said it was an alignment problem. I checked and I could see my problem with the naked eye but they make a laser tool to check alignment- it runs from $70.00- $100.00 depending on what brand you get. It will be tight but you could possibly use a straight edge from pulley to pulley.

I replaced the entire tensioner because it looked like the issue was with the pivot bolt.

 

I had a car with a belt chirp/squeak/squeal that would not go away. Turns out the crank pulley was bent and causing the belt to move sideways across the idler. Replaced the crank pulley and it was quiet after that.

 

Buy a gatorback belt! Its got like a super fine felt to it! Works great on all my stuff! Keep the dressing in the kitchen by the way