Cooling system problem

I have a 95 Camaro LT1 and i'm having a moajor problem with my cooling system. My radiator cracked 2 days ago so I had to replace it. I just replaced it with a brand new one and drove it about 30 miles and the new one just cracked. There is too much pressure building up and I have no idea why. I go to school for automotive and my teacher told me that it is caused by not puting enough coolant in the system but I don't think thats the problem since it suddenly happened twice. I put the coolant in and I know it was filled to the top. I pulled the radiator cap and it was rusted to hell. I thought that might possibly be the problem but my teacher informed me that it is not. Does anyone know what could be causing this? Is this a comon Camaro problem?

Eh, the cap does maintain system pressure, and if it's rusted and won't open to vent pressure, there ya go, and your teacher better find a new occupation of it is.

yeah the only thing i can think of is the cap is not working, like z28 said just buy a new one and see if it helps