One problem related to power assist hydraulic brake has been reported for the 2001 Chevrolet 2500. The most recently reported issues are listed below.
2001 Chevrolet 2500hd pickup had a complete power brake and power steering failure almost resulting in a crash as I was almost not able to bring the vehicle to a stop. Luckily no one was in front of me. Mechanic states that pump shaft had a break in it. I've still got the part if that would help with your investigation. Luckily I was not towing my 10,000 pound RV trailer at the time of the failure or I may not have been able to control the vehicle.