Somewhat amazing to see the temp gauge spike that fast under light acceleration.
Last time I saw something comparable was in a truck that had thrown the belt on the water pump (ZERO water circulation and no cooling fan). Think this can be partially ruled out in your case though.
Assuming the water pump is doing what it should and the dealer has changed the temp sensor(s) and the thermostat, any idea if they've checked the cooling fans for proper function?
I've noticed mine seems to have a variable speed depending on engine load, A/C on/off, outside temp, etc...
For example, when it's 110 outside with the A/C on and I pull into the garage, it sounds like a tornado. From there, I shut the A/C off and let the engine idle for say 2-3 minutes to cool off, and (based on sound) the fan seems to go through at least 2-3 gradually lower setting. Eventually it's either a quiet hum or undetectable (possibly off?).
So my question/suggestion is, when the overheat light comes on, does your fan sound like a tornado in a trailer park? It should still be at max if the gauge is anywhere above normal, and if not, that may be your culprit.
2012 Se Ingot Silver 5-Door w/ 201A & Se Sport Package
2001 Silverado 1500 RCLB 4x4 4.8L 5-Speed