03 1500HD 6.0L going into "reduced Engine Power" mode.

What is your question?

replaced throttle body and wiring harness and pedal position sensor. Happens at all different times and conditions. you have to pull over and let sit a few minutes then start back up and runs. Please help???? What could it be? Code reader says dealer specific code but they just want to keep changing parts and charging fees with no resolution. I see plenty of these on the road and know I cant be the only person with this issue. I have tried everything suggested on the internet so far. Please help?