Have an '89 6 cylinder automatic that after driving for about half an hour will at times as I slow down for a corner or light will drop rpm's suddenly and shut down. Can be very scary at times depending where I am but when I pull over and try to fire it up again it won't start. Radio works etc. It takes 20 or 30 minutes before it starts up again. Also, after a short drive another time and pull into the garage the overflow tank gets full and fluid at times is bubbling. No leaks and hoses seem okay. On this RS model 2.8L the thermostat is difficult to access without removing many things. Guess that would be the best place to start for this problem. Would appreciate any ideas, thanks.