It comes down to what are you towing.
If you drop down to a 10-12k 5er, I would probalby lean towards gas unless you do an incredible number of miles.
By the time you get up into the 16k range and then load up for long trips, diesel starts making a lot of sense.
A few thoughts on some of the comments:
- Longevity is really a non-issue these days unless you are a big rig putting 100k+ miles per year on the engine. Properly maintained, either engine will hold up long term.
- Diesel engines have more torque but gas engines are happy at higher RPM. You simply use a lower gear ratio to get similar torque at the rear wheels. It sounds like the engine is screaming but assuming it is in good repair and within the tow ratings, it's fine.