Did a subaru dealer put the radiator hoses in? If so they would definitely have been done right, but if a standard mechanic did he might not know. Our coolant systems are intricate and easily prone to developing air bubbles. Too much air in the system can cause overheating fast. Take the cap off of the coolant overflow just above the turbo and start the engine when it's cold. Let as much air work its way out of the system as you can. Repeat this a few times, topping off the coolant resevoir if it starts to go down.
This is the most obvious problem I can think of, anyone else have any suggestions?