F350 21,000 miles oil& filter change with fuel filters replaced. Customer drives 20 miles hooks to horse trailer goes 50 miles truck starts acting up. Check for DTCs one hard fault three memory for accel. pedal, replaced, no codes return. Truck has a fluttering type noise in intake and air filter box also surges. Only between 1700 & 2000 rpms on steady pull with or without trailer. Truck has manual trans., doesn't matter what gear. It's like turbo is working then shuts down real quick. It will do this 5 or 6 times real fast, almost like a buck and jerk. Again no codes, hotline says engineering is working on a fix for 04 & 05. Hotline also said it was normal at that rpm. It never done this for 21,000 miles, how could it be normal!!!!