2001 ford windstar

my van randomly started overheating on my way back from a trip a few hours from home. i stopped and popped the hood and it was pushing antifreeze out of the flood hole in the reservoir tank. this same day my a/c stopped working. I thought maybe for some reason it was just low on coolant so i filled it back up and took off once it cooled down but drove around the back roads off the highway before getting back on. I reached about 50 mph for about 15 minutes and had no problem so i got back in the interstate and a few miles down the road once i was going 65 it started to overheat again and pulled back over. I then realized that if i went below 60 mph then it wasn’t going to overheat. I set cruise control on 58 mph and went to the closest auto zone that had a coolant fan relay for my van and replaced it. i drove 200+ miles at around 70 mph with no problem at all, i was thrilled i fixed the problem. WRONG. It started overheating AGAIN. This time i was paying attention and it didn’t get too hot so the antifreeze wasn’t coming out of the reservoir tank. I let it cool back down and just went 58 mph for the last hour home. Why did it overheat again after having worked for 200 miles, other than changing the relay is their another step i should have taken?