2010 Prostar Squealing

I have a 2010 Prostar and I'm getting a squealing noise when my clutch fan kicks on. I had a local shop look at the truck several times and they keep saying its a belt and pulley issue. They've changed both of my belts and replaced all of my pullys and tensioner. They even put a new fan hub in and it's still making the noise. Granted, the sound isn't happening as frequently and when it does it's for a shorter duration of time since all of the parts have been replaced but the noise is still there. Any ideas?

 

I'll ask the guys at the shop. When the squealing starts the fan spins slower. Once the noise stops the fan speeds up. I also got white smoke coming out the stack when I'm upgrading a hill.