Fighter pilots only need oxygen because their aircraft are not pressurized. Why do airline passengers not need supplemental oxygen? Because the air in the cabin is pressurized to a level where the human body is still getting enough oxygen in each breath. The way the air is pressurized is exactly the same way a turbocharger pressurizes the air for the engine. In fact, smaller piston engine pressurized aircraft bleed some air off the engine's turbocharger to feed into the cabin to pressurize it so the occupants can breathe without supplemental oxygen.
In theory, up to 10,000 ft, the tubocharged diesel is going to perform the same as it did at sea level. Think about this though...if you had a long, flat road at 10,000 ft (not common), the motorhome would encounter much less wind resistance and therefore need less power to mantain the same speed. So your power to drag ratio at altitude is much better than sea level. Just something to think about.