I think it comes down to how much time you will spend towing the trailer versus driving the truck solo.
This year was a little unusual for me since I towed 4,000 miles (includes a trip from NY to FL) but most years my tow distance is maybe 10% ~ 20% of my driving. The other 80% ~ 90% is regular commuting. For me making the jump from a 5.3L gas to a 7.3L diesel wouldn't make sense...but that's my opinion.
The more the tow percentage increases the more it would make sense in my mind to make the switch but I'd have to be in the neighborhood of maybe >30% to start thinking about making the switch.