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The engine is but one factor. The transmission and drive train and frame strength and suspension and rear axle and bearings and brakes and other components all must be up to the task.
There two gains with a diesel for towing are having maximum torque at 55 mph speeds and having the exhaust brake to control speed going down a steep grade. I could add diesel extends the range on a tank of fuel but it is offset by having to drive further to find a gas station that sells diesel. On my travels with my diesel truck I spend a good deal of time planning fuel stops and verifying that I can get diesel along my route.