general problems of the 2008 Chevrolet Silverado 2500

I have a 2008 k2500 diesel. The vehicle is used strictly for camping and has only 24,000 miles. Over thanksgiving,I parked vehicle in an off road park. After 2 days parked, I started the truck and had no steering or brakes at all. This had happened several times before but not as bad. After a few minutes idling, steering and brakes came back to normal. I researched the web and found this to be a common problem. Gm has issued several tsbs on the subject and the claim it is "normal" on 2500 series trucks. Nhtsa has also chimed in with NHTSA id number: 10335581. I took the truck into william l. Morris Chevrolet in simi valley, CA. The service writer ignored any of my research, the tsbs and the NHTSA info. Instead, they want me to pay $780 to replace the power steering pump, when gm says it is a normal condition. I believe one of 2 things - we have a serious problem that will eventually hurt someone or they are duping people into an unnecessary expense in replacing the pump. I am an mech engineer. I asked them to show me the results of the pressure test and they could/would not. I asked how they arrived at their conclusion and was told "years of experience". I have 14+ years of experience with hydraulic pumps and am quite sure the pump ias just fine - maybe underdriven but otherwise fine.

Backed truck out of garage had no power brakes nor power steering. As tow truck driver loaded vehicle on his flatbed truck to take it to the garage (under warranty) he put vehicle in reverse, had a slight brake application then he felt a clunk (vehicle jerked). Power steering & brakes started working normally. Garage could find nothing wrong.