ok so i am new to this thread and need some help....

i have a 1995 gtp that is giving me some problems...It was overheating so i went and got the coolant flushed, which seemed to help it out and stopped it for like a week. Well, One day i got in my car to go home from work which is about a half hour away, and as soon as i got on the highway the cars temperature skyrocketed almost to the red area which was surprising because the highway is not even a mile away and it got hot so quick, i pulled over and shut the car off but started it right back up and the temperature was all the way down to the normal half way spot or lower within seconds. So i did that a few times until i stopped and waited for the fan to come on and then it drove home fine the rest of the way. After that incident, i had decided to take it to my mechanic and left it with him to drive, unfortunately, it did not do the same for him. I got the car back drove it for a few days and up to work and then again it decided to overheat well on the highway, so i got off without stopping and it dropped back to normal. I am not sure why it is doing this, but it also does this after i start off pretty quick from a dead stop or put it in passing gear. OR SOMETIMES IT DRIVES FINE THE ENTIRE DAY. PLEASE HELP!!!