I started RVing with gas engines the icon says it all...I now have a 3/4ton diesel (cummins) which I bought new in 93 and haul a 10ft camper with, it is still going strong...Too make a long story short, the diesel out pulls out hauls out performs in every way including fuel consumption...Last year my wife and I bought a new 5th wheel, 32ft. and rather than put a hitch in my truck for a one way trip to it's new home we rented a truck (one ton GMC duramax diesel with an Allison transmission and the trailer towing package) What an impressive beast it was...set the cruise at 110 kmph going over the Coquihalla and it never slowed down over any of the hills... touched the brake pedal on the down hill sections and the engine brake took over...Needless to say if and when I purchase a new truck it will be a diesel...Gearing in the rear end is critical when pulling anything, whether it be a gas or diesel engine...My brother in law has a newer Cummins and he has nothing but praise for it...he also pulls a 31 ft 5th wheel...If you are buying larger than 33ft I think a one ton would be a better bet, but if you stay 33 or below then 3/4 is fine...really depends on weight of trailer/fifth wheel.