Welcome to iRV2 , the transmission options are specified by the coach manufacturer and installed by the chassis builder .
To save a few $$$ some manufacturers will order the lower series trans (2100/2500) instead of the 3000 . I believe Monaco used the 3000 series in 98/99 production with the 5.9 ISB , but for later coaches it's crawl under to find out, if build sheet not available .
Most all coaches with the ISC will have the 3000. because of the bigger engines torque.
What years are you looking at ??