Yep, the TRX is one, and the other a 3500 (since it's for towing) cab and chassis.
Since the towing trips are generally 300 to 1,400 miles one way, it is nice to have the extra room in the back for clothing and stuff. I can make 1,400 miles in a (long) day, but not 2,800 without stopping for a while.
Of course, I'll stop either way to load or unload a vehicle, since that's usually what the trip is all about.