by this time I'm sounding like a broken record...BUT....our engine & trans is set up for COMMERCIAL / Professional weights....built for 1M miles plus (in frame overhauls & inspections aren't called for until 700k miles) and the drive train & engine is built for 80k lbs GCWR.
with horsepower/torque STARTING at 450/1650 (no premium) and going all the way to 650/2200+ with 12 and 13 speed AUTO transmissions (and optional duel drive axles) our coaches are BEASTS in the mountains (even when towing)....6 & 8 speed allison (torque converter) automatics are available too (but why bother).
we also benefit from lower labor rates/times compared to pushers (easier access to the engine, etc) our coaches can be serviced by any truck stop (quickly and have widely available / common parts because of their large manufactured numbers....no need to go thru the coach or lift the coach.