It's 110 in the beautiful AZ sun and the car starts to overheat after driving 10-15 minutes. The overheating is very slight, in the 220-225 range. The gauge will linger just above half way when on the freeway or driving around town. It never really climbs. Radiator, main thermostat, and coolant completely replaced/flushed about 2 months ago (used to work at Firestone, got it done properly by one of the techs I trust). Coolant temp sensor has about 1.5-2 years of life on it (Beck/Arnley).

Here's what I do know:
No visible leaks at all. Spent a lot of time looking around with the car parked both in the morning and after driving for a while.
Fans come on. The cooling fan module was also replaced about 2 years ago.
With radiator cap off, can clearly see water circulating. No whirring noises or weep hole leaks from water pump.
When burping the radiator (using the cool radiator funnel tool), I don't see any oil sheen, bubbles, boiling, etc from the coolant.
Coolant in the overflow stays at a relatively consistent level.

Any ideas? The only thing I can think of that may be failing is the Water Control Valve aka second thermostat. Anyone have experience replacing one of those? Or could it be the "new" thermostat has failed?

Found this with regards to the water control valve. Just FYI for anyone researching.

"Well, it's kinda complicated. The factory service manual does not state that the water control valve can cause engine overheating. However, if you look at the cooling system diagram below, you can see that if the water control valve is stuck in the closed position, the water in the engine block has nowhere to go. This blockage caused by the closed water control valve would then prevent the block from cooling. Do I think this would cause the vehicle to overheat? Probably, but not severely, the cooling system can operate normally with the water control valve closed. The main purpose of the water control valve is to allow the engine to warm up faster from a cold start. The only way to check if the water control valve is working is to remove it from the vehicle and do a boiling water test."

Going to update this since I think I may have figured it out. Short version; I don't know.

Long version, I just kept burping the cooling system and ran more distilled water than coolant. Seeing as water is more efficient that coolant at cooling down the engine, it may have contributed. I will most likely be replacing the water pump for fun but other than that it's running and not giving me any issues this week.