The ISC engine does not come in a 400 hp version. If you have a 400, it is an ISL. If it is an ISC, it is somewhere in the 330-380 hp range, depending on year and engine configuration.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC