Engine stalling

While driving at about 65-70 on the highway my car will jerk a few times and lose power. After that the engine will shut off. I know because I'll lose braking and steering power. I'm pretty sure this is the engine going into safe mode to protect itself. (As described in the manual)

The issue here is that my temperature gauge reads dead center the whole time. So I have no way of knowing the issue is coming on.

I've checked for coolant and leaks. Looks pretty nasty in overflow tank. But is to totally full.
Electric fans kicks in and runs when AC is on.
Oil looks fine. Not milky. Right where it needs to be.

I'm not sure what could be happening here but I guess it could be thermostat, water pump, or partial clog in the radiator.

Any way to trouble shoot these and pinpoint it exactly?