The hose size is fine.
Are you running a restrictor on the oil inlet side? Check with the turbo manufacturer, you may need one.
What is the drainback angle on the return line? Does it have a good drop on it?
One thing that can happen as well is crank case pressure can prevent the turbo from draining. Make sure you have breathers or a good pcv system.
HTH
Awe man.... It was just getting to the good part, too! :thumbup: