Overheating Issue

I have a 1998 Mustang GT. I recently changed my radiator because I was told that it was bad by a Ford Dealership here in Central Florida that it needed replacement. They had bypassed the heater core because it blew and I dont have $1000.00 to have that fixed. So I got a new Radiator and disconnected everything and put it back together. I filled up the radiator and ran it and let it sit overnight and in the morning I saw that it had emptied (No signs of leaks on the floor) I filled it up again and ran it (idle) and then noticed that more coolant had gone. I basically did this two more times and now noticed air coming from the top radiator hose and then purchased a new clamp because the old one was bad. Oh BTW, I bought the dye to check for leaks and it did not change colors. Wheew!! So most recently I added some more fluid and it still overheating. Could it be that the water pump? Should I change that?

Also, this car doesnt come with a bleeder for the air so I ve only put in about two of four bottles of 50/50 coolant so far and I read that the car takes about 3 and 1/2. So Any help would be greatly appreciated.

I fixed my issue very simply... I filled the reservior and continued to let me car heat up and found out that when it cools down it sucks in the fluid from the resevoir. I did this about 3 times total more till it stopped pulling in and ultimately it did not overheat anymore. I didnt realize this but the motor takes about 12.4 quarts of antifreeze. I was amazed at how much... Runnig great now and very cold. Does not go past the "O" on the gauge. I found my replacement radiator on ebay for 67.00 with free shipping and it works awesome. Fitment was no issue and it was pretty much plug and play.