1995 Chevy S-10 Run too hot too drive

I have changed thermostat twice. The oil looks ok.
The water moves inside the radiator. After I changed the 1st thermostat it seemed to start working but did not. The engine begins to run hot slowly. It will go up a little stay there then go up a little more etc. It finally reaches a temp. Too hot and I have to pull over and shut engine off and let it cool. I will turn heater on and it will keep it from getting too hot for a little more time.