There are several Cummins manuals that apply to our truck CTD. I have several that discuss the engine, trouble codes, etc. But I think you probably want the DC manual, at least at first. The DC manual covers the whole truck, the Cummins manuals obviously cover just the engines.
Oops - the new spell checker doesn't know how to spell Cummins - it suggests Cummings. That's got to be fixed pronto. It doesn't handle contractions too well either, even its own! Still a very good spell checker.