The new Ford 7.3 has really hit a sweet spot for RVers. Now with the 7.3, it can easily handle loads up in the 15k lb load. Mine is actually rated at 20k. Before the 7.3 over 10-12k lbs you really needed to look at a diesel.
With a diesel, short trips are horrible on the emmissions systems, and they don't get up to operating temps for the emissions to work properly, and those systems are expensive to repair.
The diesel is about $8-9k more expensive upfront. The old theory of getting that money back when selling is no longer true. If you run identical 2020 7.3 and 6.7 trucks through KBB, you will find the diesel is only worth about $5k more, so it looses half the cost of the diesel in 5 years.
TFL did a YouTube video of the 7.3 pulling 16k lbs up I-70 over the rockies, and it was able to maintain the speed limit of 65mph up the grade, and still had more power available to accelerate.
With the gasser you have about 700lbs more payload, my SRW f-350 has 4200lbs of payload
If towing real heavy loads, the diesel wins, but for the typical RVer the 7.3 is a great choice.
If you do uphill drag races towing 15k lbs, the diesel is the way to go, otherwise go with the 7.3.