Since all your parts are new, I'd make sure there is no air left in the cooling system. I wouldn't guess a brand new oem tstat is bad. Fan clutch can get old and weak. Look to tech to see how to test it. 30 to 50% coolant is right. I'd throw in a bottle of water-wetter (not that this is part of the problem you describe) .... Yes, being in Phoenix has an effect. Above 100 deg ambient, any small defenciency in the cooling system will show up.