I have oil in the coolant. I have the heads off and the gaskets appear ok.

Now you're positive it's not transmission fluid mixed with coolant instead of engine oil? .. Pretty common for the transmission fluid cooler to repture inside the radiator .. Just saying ........ Engine size is always helpful especially since there are 4 engine options with 2 different cylinder head configuration possibilities! .. Transmission fluid or engine oil pressures are always more than the coolant systems pressure.. When the engine is running! (Check the transmission fluid)