99 clk shuts off when driving unexpectedly


We have a 99 Clk Coupe Mercedes that has been a wonderful car....until recently when its been hot out while running the ac the car would overheat a bit and then shut off and not start again until a few hours.... however  since that we've had the radiator flushed, new thermostat , new crank shaft position sensor  and a new transmission all new.... it runs great but last pm again ...getting off of the freeway on a ramp with no place to pull off the ramp safely it decides to just shut off.   Luckily nobody was injured but right after we get it pulled off the freeway ramp it starts up and run it home???? WHAT IS IT CAUSING IT TO DO THIS?