Posting this here, as it's specific to AZ heat as it pertains to your question;
Just got back from a 3k mile road trip which included 6hrs of desert (Flagstaff to Albuquerque) and back. I noticed a few things, but first my setup;
1. New TYC 1918 radiator installed last year, $127 on Amazon. New OEM radiator cap, new hoses, PHH, Heater Valve and various small hoses. Fresh Toyota Red, 50/50 mix. New Thermostat, Water Pump installed earlier this year.
2. Blue fan clutch, unmodified, OEM fan original to the 1996 truck.
3. New Factory short block installed in Feb, rebuilt head, valve lash set, etc.
Cooling performance at highway speeds - Ambient temps over 100F, IAT around 160F;
1. No AC load, temp stabilized at about 185F over level ground
2. AC on, temp stabilized at about 192F over level ground
3. Hill climbs dramatically increased temps, longer durations pushed it up to 208F
4. Turning off AC at bottom of the start of a climb helped to keep temps down, turning AC back on during the downhill portion helped. When above 210F, I'd let the truck coast downhill which quickly dropped temps back to 199F or so.
5. As outside air temps climbed above 110F, engine coolant temp rises, stabilizing at about 212-214F at 72mph over level ground. This was concerning, and I limited AC use to keep it from rising.
On the trip back to Phoenix, Camp Verde has a hill climb that routinely tops out cooling performance. It was 117F in Phoenix, and this climb brought my temps up to 220F, AC off the whole way and STARTED the climb at 212F. Slowed down considerably, kept my RPMs up the whole way, and it didn't stay at 220 for more than a few seconds, quickly dropping down again to 214F for the rest of the climb. Over the top, it dropped back to 204-206F for the rest of the midday drive home.
I was expecting better cooling performance given the recent replacement of nearly everything related to the cooling system, combined with a new OEM short block, but there it is. It runs hotter than I'd like, but not enough to scare the pants off of me under normal conditions. On climbs, it definitely helps to have a live monitor of coolant temp data to help you adjust your driving style.