I know you have a 5.2 so its a little different animal than my 4.0 but I live in Havasu and its even a little hotter here than in Phoenix and my temp never goes over 210 in even 120 degree heat with AC OFF but when I turn the AC on with temps outside of 95 degrees or higher, if the engine is under a constant load like driving uphill for a few miles towards my house the temp gauge gets up to close to the next line after 210 and I just shut my AC off then since I am almost home within a couple miles anyway. I never really wanted to see how high the temp would go lol.
Hopefully you can get something figured out. Im at 144k miles still on stock radiator for sure and thermostat too as far as I know. Reman water pump replaced about 26k miles ago. Our factory cooling systems suck in high temps...
so i disconnected the down pipes (well, the passenger side one, i couldnt get the exhaust to drop low enough to disconnect the drivers side) to release backpressure and ran it for about 30 miles at highway speeds. temp never went above 200*!
time to PM Kolak about a cat
Reliability is relative