My dealer said it was because the turbo was spooled up it was using more fuel. What is crazy is I traded off my 22 3.5TT Tundra for a 5.7 Tundra and I'm getting better mileage in every type of driving (towing, highway, city).That's not the turbo causing the drop in MPG, it's physics of drag. Heat engines are heat engines. Turbos don't result in inefficiency at speed.