We switched from an old 7.3 diesel to the gas V10 with a similar size 5th wheel.
Both do just fine. Yes, the newer diesels will win a drag race and we dropped from 12.7mpg to around 10mpg (still dialing in the V10 numbers).
But with the up front costs, you will never justify a diesel in a new truck financially.
The reason to get a diesel is you are towing a load the available gas engines can handle...maybe a smaller load if you plan a lot of mountain driving where the turbo makes a difference (if they start putting the ecoboost in the 250 that changes)