If the coolant level is low then you are likely burning coolant. The engine will not run hot because the water pump is still circulating coolant but some is getting consumed in the cylinders while it is running. The likely cause is a cylinder head gasket like Jay said or a crack in the actual cylinder head. Unfortunately you cannot smell the smoke to tell if it is coolant or fuel caused by a broken injector. The low power issue you mentioned makes me want to say it is a fuel issue. Either way Ford will be able to address the issue, good luck. If you have any questions feel free to ask, I am in the heavy duty diesel engine industry for a living.