I just bought a 2004 Sebring base model with a 2.7 that is overheating. The owner was told by a shop that it needed a head gasket. I've done a compression test, and a block test (the one that tests for exhuast fluid in the coolant), there was no loss of compression between cylinders, and no exhaust gas present in the cooling system. I did a pressure test and saw a 3psi drop in 20 minutes. I also bled it. What should I look at next?