Car overheating

Hello, same little red Nissan as before here. I am having overheating problems. I recently got the car back from the shop after they replaced the fuel pump and hooked up a switch to turn the fuel pump on manually instead of me looking for another computer. On the way home I noticed the needle was going up. Not very very fast but it still was overheating. I looked in the coolant reservoir tank it was overfilled. It looks like it is pushing the coolant out or it is being backed up into the coolant jug. Next day I drove it without the AC and it was doing fine, but after two hours it eventually started overheating again. I turned on the heat while I was driving to see what effect that would have and it surprisingly cooled the temperature down. The car's radiator is full of coolant and once the coolant jug went back down it is now at its normal place below the line. Any suggestions before I go spend more money?