The dealership I work for is a heavy truck dealership. Unfortunately, the gauges in our trucks are quite accurate. Trucks show up all the time, already pre-diagnosed by the owner. "Yeah, I need a turbo because my boost gauge is down 2 pounds on hard pulls." Oi. Then comes the painful process of explaining electronically controlled VGTs and the dozens of factors that help the engine decide how much boost it needs at any given moment.
Check out the ridiculous number of analog confusion devices in the typical truck we sell:
http://www.peterbilt.com/uploaded/ne...Package-lg.jpg
They should scrap most of them. If something is wrong, the check engine light will come on. If something is very wrong, the stop engine light will come on.