I recently purchased a 2005 6.0 It has an air intake and a catback exaust. Now I tried to pull a small bumper pull trailer, less than 5k pounds..i was able to reach 65 mph at first then it dropped down to 50 mph and i could not go any faster than that. When i tried to accelerate the turbo would not spool at all but the rpm would go up to 3000 and the truck just made noise but no additional power was given to the wheels. I pulled over and let it idle for about 10 min and the truck took off fine for the first mile or two and then did the same thing again. The truck never overheated and never threw a check engine light.
Could it be the turbo? maybe the cooler for the turbo isnt working? also if i am at a stop and i floor it, the truck takes off slower than if i were to give it half throttle?