I've never really had trouble bleeding the stock system, (provided the thermostat was good and installed properly), but I did have issues like yours when I installed a Mishimoto radiator.
Like you, I never experienced an issue with overheating, but I did notice some coolant disappearing. I had a feeling air was still in the system, so I did the following:
-Opened the coolant reservoir by the turbo and stuck a tall funnel in the top to catch overflow
-Turned the heater on full blast
-Started the car and let it get to FULL operating temperature, revving it up a bit once it was fully warmed up. Once the thermostat was open, I got out and "burped" the upper and lower radiator hoses as well.
I saw a lot of small bubbles for quite a while... for a moment I was paranoid I might have a leaking head gasket. But then, after about 30-45 minutes, it stopped.
After that, I pulled the funnel, replaced the cap, and have used next to zero coolant since. All I can figure is that it's a big radiator, and as a result getting ALL of the air out is a bit more difficult.
Hopefully you are dealing with pretty much the same issue.