I have the EXACT same problem with my 2005 Tahoe when it is cold out like below say 30 degrees or so I think I know what you mean... Squealing noise when cold and when it warms up it goes away. Colder it is out the longer it takes and goes away slower right? Summer time 100% gone.
I know metal does expand and contract with temperature, so wondering in summer it is expanding that little bit where the noise is not there. Weird I know, but it does that.
Only when it is cold out and I got it at the end of last winter and did some work on it during the summer. Figured with age time for a new belt and keep the old one in the back cargo compartment due to having a used one in the future if it breaks is better then being stranded. Always good to keep the old one for a just in case.
Changed the idler arm as well with age and thought I had it for sure when I changed the pulley on the A/C due to it sounded like crap. I could hear it growling slightly when it was warm out doing the work so I put it in a bad and tossed it in the freezer to simulate winter. That made it 100 time worse and got the new one and it spun endlessly where this one barely made it around 2 times.
I did check my power steering fluid before all this and it was down and added some. I figured it had a leak and checked it about a month later and had to add a little bit more and put some of that stop leak in. It stopped the leak and that is all good, but wondering if that had some effect on the pump. I know you said you changed yours, but I learned this and even from my mechanic that when you get new parts they are not always good. He has had new stuff come in bad all the time and even turns new rotors and got some worse then what he was changing due to they were warped. He is beyond awesome and checks many parts due to he has the know how before he puts them in.
I am have been driving my Suburban and tomorrow hopefully I can start it up and get the pipe out, old mechanic trick but you have to be careful.... I take the pipe and put my ear to it and put it by components due to it will amplify in the pipe and isolate where the sound is coming from. MAJOR safety is you got to watch what you are doing due to that pipe gets in the belts and HUGE PROBLEM. I know my mechanic has a medical stethoscope, but took off that part and just uses it to go in his ears and put a small pipe on it so he could watch what he is doing.
Our problem could be the same part of a different part and you changed a bunch so far and I was thinking alternator or power steering pump, but who knows could be wrong. I will post back on here with what mine is if I figure it out or if I take it to him due to he will figure it out for sure 100% guaranteed.
So once again not saying my problem is the same as yours parts being bad wise, but you never know.
Just like above just because you get a new part does not mean it is good. He has seen that many times and I have now twice.
I will keep you updated...