While driving engine shuts off

It's been awhile since I've messed with this car. I bought it and it was this way when I bought it. I have pulled the codes up on it and it was showing the throttle body code on it. I replaced the throttle body on it and now it pulls a code up it will not read the throttle body. I took it the Chevrolet place to have it programmed and it doesn't program through the computer it will rev up real high 2500 3000 RPM's when it warms up some it'll drop down too 1000 to 1200 RPM's. Here while back it wanted to run hot replace the thermostat in it thought that would might be it the trouble with it did not fix my issues. Now you can drive it down the road the hotter it gets the worse it gets. It will shut off it'll start back up. I will mess with it some more here in a few days and try to get some codes off of it and get back with you the security light will flash like three times going down the road and it will shut off. The Chevrolet place tells me there no way that car can be doing that because that security system is just for startup.