Loosing coolant

[Boog]

My 06 crew cab with 5.3 has been loosing coolant for a few months. It's been gradually getting worse. So far I have not been able to locate the source of the leak. I was adding a quart a week and it's now up to near a gallon in less than a week. It does not drip on the concrete. It's not leaking from the heater core inside the cab. It doesn't appear to be getting in the engine oil. About the only place left for it to go is the combustion chamber. We never smell antifreeze. The engine runs great and we get no codes. It has about 130,000 miles on it. The one thing I have not checked this week is the tranny fluid. If the coolant was getting into the tranny cooler the fluid would register high and surely by now it would start slipping and acting up.