It's not possible for us to diagnose your problem over the internet! I would do a leakdown test on each cylinder to check sealing and go from there.
Can I ask how much the parts and machining were to o-ring the block? I am considering going down that road. Also, did you use a copper head gasket sealant during assembly?
Good luck! and be careful to ensure that your coolant does not become corrosive, I have several 7M heads that are no longer usable due to corrosion in the water jackets.