Nothing like having the passing power of a diesel. But I'm one of those guys. They are making huge strides in gasoline powered vehicles lately. I'm pretty sure there is a fuel economy war going on, even if it was meant to be a work truck.
Say what you want about not caring about fuel economy on vacation and all of that'. Personally, when I have to fill my tank it's very disappointing. I hate seeing 10 mpg average. I just feel like we have come further than that by now.
That been said, if you don't mind your truck going up a grade a couple of gears lower and your motor singing at 3500-4000, as well as a little poorer fuel mileage (and not much really), then you can save yourself an easy $8000 new. That's something to think about. Gas powered trucks are quieter, probably more reliable, and maintinence costs less and is easier to perform yourself. Gas vehicles have injectors too, and they can go out as well. But the chances of getting poor quality gasoline is far less than for diesel. It's just nasty stuff.
As far as new vs used, find what you like and test drive it all. I'd be surprised if a seller wouldn't let you hook up a trailer or throw some weight in the truck and test drive before you buy. Reliability with newer diesels I still feel may be an issue. Don't get me wrong, if I had the money id have a brand new ford or dodge diesel in the driveway tomorrow. But they still have a lot of extra emissions stuff that isn't proving reliable long term for the average consumer. What I mean by this is if your truck is a daily driver 13 miles one way, then it's probably not getting up to proper temperature.
Just things to think about. Again, impressive things coming out for gasoline. The newer motor in the Rams seems to be a good deal for a vacationing truck. And way cheaper of a truck out the door. Still more stations carrying gasoline than diesel.
Take your time in finding the right one.