"dadd".....Your coach engine would barely push along a station wagon without a turbo. The turbo is what makes these diesels go. The turbo pushes air through a CAC (charge air cooler) which is just a big aluminum radiator. It's typically similar in size to the engine radiator. The turbo is pushing air through that system at pressure. If it develops a leak, you will lose power.
If you're handy and physically capable, you need to look at your engine and follow all of the trbo connections and check for leaks. There is a very stout hose clamp with a large tension spring built in at every connection. You're looking for good/tight clamps. Typically, if they're leaking, they leak black soot and can be obvious. The last thing to check is the exhaust manifold, looking for cracks and black soot.
Hopefully you just have a loose or broken clamp.