94 S-10 shuts down at 210 degrees

I have a 1994 S10 w/107,000 mi. V6 Vortec motor, auto trans. Have started to experience a very strange thing. Any time the engine temp goes to or even gets near 210 degrees, the motor shuts down. I thought it was an overheating problem, so I flushed out the cooling system, was a mess, but that part of it is now fine. Still happened. Removed the T stat (I live in Vegas, very hot here, this is a very common thing to do here). It takes longer for the engine temp to reach 210, but if it does, it still simply shuts down. I also replaced the coil, thinking that it may have aged and become faulty, nope, that didn't do it either. Even if the truck has been running ok, and you stop to run in to a store or something, if the temp gauge goes up to 210 degrees (sitting w/o running) it will not start untill after sitting for about an hour to "cool" down. Someone told me that the auto choke/shutdown relay might be going bad, but I have not a clue as to it's location, it is not covered in any of the common manuals, I know, I have enough of them. Signed, Very Frustrated!