Grand am spewing coolant...Help!!!

After driving for 6 hours for no problem, i get home living at the top of a long drive up a vermont mountain (Killington) to pull into my driveway, shut the car off and coolant leaked out of the overflow spot in the reservior bottle. The car did not overheat but was probably warmer due to the long trive up the mountain and head gaskets and waterpump have been properly replaced 2 years ago. I added water and drove it around a bit and everything seems normal. Any suggestions on the possible problem please help me out.

Welcome to AF.

Its possible it was due to going up hill ,
when the reservoirs drain is in the rear.

I'd keep an eye on it though just in case.

I dont see a year model but many grand ams have weak coolant systems. If it has been two years since your head gasket job it is probably time for a full flush and new antifreeze (antifreeze does wear out and if you dont have the proper mixture it will get hot because water boils at a lower temp). Flush it fill it keep a close watch on it. Make sure you use 50/50 antifreeze or dilute with distilled water.