Something to think about, EVERY RV hauler thru the approx 20 yrs I've posted on here, has mentioned non slide 5w trailers with smooth fiberglassed walls get the best mpg for a given wt. Worst is a TT with corrugated aluminum siding. Best aerodynamic setup vs worst!
With this said, power wise, I'd be surprised if the 6.0 could not pull a 10-12k lb trailer over most freeway, st highway type roads. As also noted, take into account HP loss for elevation. You WILL go slower at higher elevations.
Chassis wise, a 3500 be it diesel or gas, assuming same payload etc, will generally speaking handle the trailer the same. Power wise, diesel will win generally speaking due to a turbo at elevations etc. Depending upon how many miles you tow at elevation, for me that is around 6000 ft or higher, will depend upon if I need to spend the PREMIUM for the diesel.
For me any how, I would not spend extra on a diesel, the 6.0 with a properly speed low aerodynamic trailer will work fine in 80-90+%, of the situations I get into.
Marty
