There is absolutely no doubt that a diesel makes for a better towing experience, even for a lighter trailer....they just work super!!!
My buddy and I had to got to Arizona to tow his 13,000# 5th wheel back to Illinois. His F250 6.0 diesel was phenomenal towing the unit, and got a solid 11.5 mpg for the entire 1500 miles.
I had a Cummins a few years ago and loved the towing capability.
However....there is a lot of extra cost to a diesel. My buddy's F250 had to be head studded at 80,000 miles, and needed new injectors....cost was almost $8000.
A neighbor had his turbos go bad on his 6.4 L Ford diesel....almost $10,000 with all of the associated repairs, and he was just out of warranty when it happened, so fairly low miles.
A new diesel truck will cost $8-$10k more for the engine....and fuel seemed to be about $.60/gallon higher most places we went. Used diesels have the potential of super high cost repairs.
If I was on the road all the time, I would certainly go for another diesel. BUT, I tow 5-6 short trips a year, and maybe one long trip over 1000 miles. I get 7.5 to 9 mpg, and I struggle a little up some of the steep hills, but I cannot justify the cost and maintenance of a diesel....and the DEF fluid (just one more thing to take care of).
My nephew has a super cool Cummins 4x4 with a big lift kit and has never towed a thing....he just loves diesels!! Not at issue.
Some folks LOVE them, some folks NEED them, and some folks have to decide if the hassle and expense is worth the cost. I personally do not have a need for a diesel, don't want to spend the money to own one, and don't was to pay extra for the fuel costs.
Good luck whatever you decide.