97 3.4 DOHC Monte Carlo PROBLEM!!!!!!

Ok where do I start? Uh Well I bought this car 2 years ago and it was reading hot on the temp gauge the day after I bought it! I took it back to the dealer I bought it from and they said everything was fine and that it did not overheat on them! But I have been driving it for almost 2 years now with it going hot and back down. Well about 2 weeks ago the thing really started overheating and seemed like it would not cool down. It also would hesitate reel bad too like it was gonna stall. Well I've had a dealer recently tell me it was a head gasket but i'm confused. Let some air out of the bleeder on top of the thermostat and drove it for 20 minutes and now it won't overheat. I'M SO CONFUSED SOMEBODY PLEASE HELP ME IF YOU KNOW ANYTHING!!!!!!!!!