possible head gasket leak

Putting pressure to the radiator (performing a pressure test) will not expose a head gasket issue. You'll need to determine if there is exhaust back pressure coming into the cooling systems. Are there any hydrocarbons being measured in the coolant? Does the coolant bubble with exhaust smell in the reservoir? These are clues - but nothing is better than hands on inspection and verifying no external leaks. Are you having performance issues? What does the engine oil look like? Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops