Put the truck in the shop for a DOT and to get an air leak fixed. At first they said there was none. I insisted that they look again. They found a small leak in a line for the lift axle, still showed air lose. They looked around and found a "quick release" valve on the lift axle leaking. Replaced that. Gauges still showed a leak. They hunted around some more. Found ANOTHER leak, this time it was the "fan hub". Needs an "O" ring kit. What fun this is!!