2nd gen chirping under load when hot

My truck has what I assumed to be a belt or pulley noise. But I have changed the belt and all idlers (including the tensioner) twice now. I have sprayed it with conditioner on multiple occations. It only happens after the engine is hot on a warm day (90* +), I live in phoenix most days are hot, and usually acceleration or pulling, with a/c on or off I get a chirp/squeal that changes with rpm. I can't replicate it at a dealership and really don't want to end up throwing a belt. Any advice?

 

So to find out what can be causing that noise I would suggest using a stethoscope that you can pick up at Harbor Freight for maybe $10. Place it at all points where the belt makes contact with a rotating object. (For obvious reasons, be careful how you do this with the engine running!) That is the only way you will know for sure where the noise is coming from. Also, if you used an off-brand, sometimes those belts just make noise. Get you a Gates belt.

 

Gates belt and pulleys. And it only happens when the trucks under load so I'm not sure how I'd listen to with a stethoscope. But I'll give it a try and see if there's anything I can't hear at idle.