overheating problems, please help!!

My 95 LT1 camaro is overheating and I cant figure out why. The Thermostat is fine, the water pump is good, and I just had the radiator rodded out today. I reinstalled the radiator and it still overheats. When I start the car with the radiator cap off, it sucks the water down some, then starts burping it back out. When i replace the cap, it pushes the water out through the over-flow jug. Is it the heads? Could there be a clog somewhere else in the coolant system? Any help would be appreciated.

My bad guys, I didnt think the first post went through. Sorry

sounds to me like you have a clog in the block somewhere...