1994 Pontiac Grand Am SE 2.3 Litter Quad 4 SOHC

I have a 94 Grand Am SE 2.3l Quad 4. I replaced the heater core about a week and half ago. After Replacing it and hooking all the hoses. My Dad drained the Jug on the side of the Radiator ( I dont have an old fashion Radiator. It dosent have a cap on the radiator, it all goes thru the jug on the side) After that The low Cooliant Light came on and it began to over heat. A friend said it was "air Locked" the next morning we messed with it, squeezing hoses and such and it began to run at normal temp (between 190 to 200 degrees) but with the heater on it runs at 220 degrees. Today I was driving to town after drivng about 5 miles it began to heat up. I turned around and went home when I started up a hill it got up to about 260 degrees when going down the hill it cooled down to about 220 degrees. I stoped at the store and when I left the store the faster I drove the cooler it ran (until the transmission shifted). In total I drove the car for about 15 minutes. When I got home I opened the hood to see if I could see water leaking. I could hold my hand on top of the motor, it was cool like the car had never been started. What could be the problem?