Driving it starts to buck and stalls and the temperature bar lights up briefly

Slight misfire. That was fixed last month code was a cylinder 8 coil pack replaced. Has another. It’s another miss fire that just started. No dummy lights no codes either. Now the car idles fine with miss fire. No code shows and It restarts after a few try’s. Rev it up in neutral it stalls. You can drive it at low speed and bucks a little.
Ruled out fuel filter, fuel pump and bad gas. My mechanic who is a P71 expect is also a Police dept Mechanic. He says the temperature bar that briefly lights suggesting the temperature censer is bad and shutting down the cylinders and engine. He also saying the transmission is failing and over heating. What I don’t get is when I floor the car it takes off fine the transmission seems fine then it shuts down.