We have a 2005 6.0 diesel 4x4 that has had almost everything possible fixed/repaired on it already. The problem we are having with it at the present and that our mechanic is stumped over is: when under load (pulling our 31 ft. Fifth wheel up a hill), it kicks and bucks and stalls out. When we pull it off to the side of the road and restart it, it runs fine. Our mechanic drove with us while pulling the fifth wheel and when this happened, the diagnostic reader he used on our truck with the laptop did not show anything but a turbo over boost but he said that shouldn't cause problem like we experienced.
What could you suggest that our mechanic check for on our truck?
Thank you for any help you can lend us.